First, I currently have a Sony str-dg510 receiver, it is pretty much the most entry level receiver Sony makes. Aside from more features/power will there be an improvement in actual sound quality upon upgrading to a better receiver?

Second, is the expected "which receiver should I buy?" lol...

I ask because I don't really need many of the features in many of the receivers. I will be powering (2) 4Ts, (2) 4Bs, (1) 5C, & (1) 8D. My use is 50% music, 40% XBox 360, and 10% movies. My source for music/movies is my pc (through hdmi) so I don't need many of the common features. Also, I live in an apartment so even my crappy Sony offers enough power, I am basically just looking for an improvement in sound quality if an upgrade would offer that in the $400-$500 range.

Any advice/suggestions are much appreciated 

I'm no expert, but don't confuse volume level with the need to drive good speakers with proper power.  Constant, proper power is essential, even at lower volume levels.

That said, a quick Googling would suggest that your receiver is rated at 100watts/per, which is a lot better than I expected.  I would question, however, Sony's efficiency.  With the exception of their truly high-end gear, the general consensus seems to be that their entry-level receivers act like it.

At that price range, I usually recommend the Onkyo TX-SR606 (or newer 607 when it comes out).  I have one of its bigger brothers, the 876, and love it.  But, everyone recommends what they're used to, so you'll see Denon, Yamaha, Pioneer Elite all show up in the "suggestion box."

Hook up your speaks and see if your ears think there is enough power there.  Just know that these speakers crave power, so you can do a lot worse than upgrading the receiver eventually.

If you want to stick with Sony, Crutchfield has the STR-DG1200 for $300 off, $599. http://www.crutchfield.com/p_158STD1200/Sony-STR-DG1200.html?c=4

 I got it but I can't tell you how good it is yet because I don't get my Aperion speakers until Saturday. If you do buy something from Crutchfield.com though, use this referral code: payy2-h9c87-ki5k2 it'll save you an extra $20 on any order over $100.

The 100 watts/per channel though depends on the brand, no?. Sony rates everything much higher than it really it is, if you look at other brands (onkyo specifically) they have $600 receivers that are just 100 watts per channel... no way the $200 sony has anywhere near the same power.

I was looking at the Onkyo TX-SR606 actually, but had read a lot of complaints about them running exceptionally hot, which is why I figured I'd ask for suggestions. I wasn't sure how the other brands stacked up in this area either.

If I do go Onkyo, would you recommend getting a 706 or 607? Both I've found for $500 shipped. The 607 has all the new features (don't really know that I'll ever use most of them like PLIIz, etc) but the 706 has more power 

And I don't wish to stick with Sony, I am a fan of Sony but mostly for video, I'm not too impressed with any of their audio equipment 

Thanks for the suggestions

My 876 runs hot, but nothing that a $10 fan can't fix.  If you're gonna keep it in a very tight cabinet, I'd worry, but otherwise, it's very manageable.

Your choice of Onkyo would be up to you, but I'd probably go for the 706 over the 607 if they're the same price.  Power alone is worth it to me.  The 607 has more HDMI inputs, but it's nothing that a switch couldn't fix if you really needed more than the 706 had.

The 706 also upscales to 1080p (vs 1080i on the 60x series), although the chip it uses doesn't have the best reputation.

It will be tough to go wrong with either.  Same can be said for options from Marantz, Pioneer, Denon, etc.

Based solely on power... would the 806 be worth it over the 606/706 considering all but 1 of my speakers are 4 series and my listening area is so small (10'x12')? Price wise i can get an 806 refurb for $600, 706 for $500, or 606 for $320. The extra $100 is no big deal, but comparing the 606/806 it's almost double

As we all do, I'm just trying to get the most bang for my buck & not regret what I decide on... so sorry to be such a pain lol

The only thing I'll say about the 806 is that I was originally going to get that, but then read about the issues with the upscaling video.  Same chip as the 706.  Google "Onkyo 806 blue dots" and you'll see what I mean.  BUT...not everyone has the problem, not everyone cares about upscaling, and many are very happy with their purchase.  Incidentally, you can set upscaling to 1080i (I believe), which not only eliminates the issue, but be equal to that of the 606's ability to upscale.

My brain was hurting trying to make a decision, so I bought the 876, which has a different (many say better) video chip, and never looked back.

I'll say to you what I say to many: Quality remains long after the price is forgotten.  Save your pennies, and get the best option for you from the beginning.

Yeah, I found those issues earlier... they apparently have it fixed in the later builds of the 806 though and it was only an issue when trying to pass 1080p through untouched as it was (from what I gather) trying to upscale a signal that obviously had no where higher to go

I definately hear you about the quality remaining after price is forgotten, I learned that some time ago. I just hate to spend the extra $300~ on the 806 if I won't be able to even utilize most of its potential. If I was sure it would benefit me I'd be ordering it right now. I'll just have to mull it over a little more I suppose... sigh

Thanks for the continuous help

So I'm leaning towards the 806, I just have one concern I just realized...

Most models (like the 606 for example) say this under their power specs... 

Front L/R    90 W + 90 W (8 ohms, 20 Hz–20 kHz
0.08%, 2 channels driven, FTC)
105 W + 105 W (8 ohms, 1 kHz, 0.7%,

2 channels driven, FTC)
110 W + 110 W (6 ohms, 1 kHz, 0.1%,
2 channels driven, FTC)

The 806 just has

 Front L/R    130 W + 130 W (8 ohms, 20 Hz–20 kHz,
0.08%, 2 channels driven, FTC)

... I don't fully understand these added specs, but it would appear as though at 6 ohms it puts out 22% more power. If this is the case, the 806 starts out at 130wpc, so at 6 ohms (which my speakers are) it would put out 159wpc which is higher than the max recommended for my speakers (150w).

I may be misunderstanding the specs, but if not wouldn't this cause a potential issue? I know with the 806 I can set a max volume, but I would rather not need to

The 606 has all the features I need, I don't need anything the 806 has that the 606 doesn't. But the extra 40wpc got me. Even if I don't need it (which I'm sure I don't) from what I gather more headroom = better sound quality. Plus the 806 is much more pleasing to the eye. I was leaning more heavily towards the 806 a minute ago so I bought it before I could change my mind

I know I won't regret it, I'll have forgotten about the price difference before it even gets here lol

Thanks for all your help PJ, I'll be sure to post my impressions once I get it. Jumping from a $200 Sony to an $1,100 Onkyo ought to make my speakers sing & dance to finally be properly powered

Now I just need to get my 8D and my system will be complete 

Awesome.  Agreed, and I think you'll be very pleased.  I'm happy to have helped.

Be sure and post pics when you get everything all set up.

So it finally came today ...

Compared to my Sony this thing is a BEAST... both in power & sheer size.

I haven't had the chance to fully play with settings yet, but I ran Audyssey (I haven't ordered an SPL meter yet) and adjusted the crossovers a little and holy crap does this thing put my Sony to shame. I was listening to some music and I decided to put it from 5ch stereo to 2ch... I literally had to get up to make sure my center/subwoofer were actually not producing any sound... my speakers have come to life! 

I then played some Halo 3 & the gunfire/explosions were so clear it made the way it used to sound seem like I'd had ear plugs in.

I am thoroughly impressed with this receiver so far, but even more so with my Aperion speakers... they were amazing when I got them but now, wow... I can't wait to fine tune things over the weekend. Oh, and I was wrong about the power ratings, at 6ohms it's rated at 180wpc

And I'll post pictures once I get my 8D in a couple weeks as then everything will be complete