Maiden,

This is a tricky subject. It involves ohms law, varying frequency inpacting impedence, and many other factors, most of which you probably don't care about (or maybe you do?). Let's see if we can make this simple......

To make a long story short, most amplifiers will handle the 6 ohm speakers just fine set at the 8 ohm setting. Usually, when setting an amp at 4 ohms, it adds resistance so that the amp "sees" it as being 8 ohm to avoid overheating. The resulting outcome is less volume. Keep in mind....not all do this, some may be designed to run the lower impedence without employing such "tricks". 

Going back to my car audio days, amp designs are all over the place. Some amps are designed to be used at lower impedences, but not at face value. I have a monoblock amp driving my dual subs. The rating is: 220 watts RMS x 1 at 4 ohms (400 watts RMS x 1 at 2 ohms). In the old days, this is how people would cheat in car audio competitions. The drawback to this is that you need more current (technically, double).

Wow! half the impedence, and almost double the power (there is that damn ohms law crap)!!! So, I run my 2, 4 ohm 10" subs in parallel to get the 2 ohm load, and double the power. Versus. wiring in series, which would double the impedence to 8 ohm, and would half the power. But, I need twice as much current.....Oy....

Now this is totally different than most home amplifiers, that are rated at 8 ohms. Car audio does that so that you can get into comptetions at the rated power (the 220 watt), but yet actually get 400 watts of actual power.

So, taken ohms law into consideration, if your speakers are 6 ohm, and you run at the 8 ohm setting, you should get more power, right? Well....maybe yes and maybe no. Most speakers are rated at "nominal" impedence. In layman's terms, this is an "average". But again, frequency impacts this, as well as other factors such as speaker length.

I am sure Hicks could get more technical than that if you want....I have not touched ohms law in years. But his advice is solid. Just set it at 8, and let er rip. The last thing you want to do is get paralysis from overanalysis. I am wayyyyyyyyy to guilty of doing that myself.

I know I asked the same question with my Onkyo 805. It runs just just fine at 8 ohms, as I am sure yours will. I asked the question, as I did not want to cook my Onkyo. Belive me, it gets warm enough on its own (btw...the onkyo heat issue is a bit blown out of proportion). Heat is a byproduct of power.

Let us know how it goes! You will love your Aperions!

BTW.....I am doing this all from memory. I have not been into the tech stuff in well over 15 years. If my info is not accurate, let me know and I will pull this post down.