Current setup:

Receiver: Denon AVR-4306
HDTV: Sony Bravia KDL-V40XBR1
STB DVR: SA 8300
DVD: JVC XV-S65

I have had the receiver two weeks. I did not yet invest in 5.1 or 7.1 speakers, but connected two pairs of stereo speakers that I have had for twenty years (but still sound fine) as follows:

Front Left and Right: Kef C Series C65
Surround Left and Right: Wharfdale Diamonds

I guess that makes it 4.0 or Quadriphonic !

Question is - will I notice a big difference if I upgrade to a real 5.1 or 7.1 system with subwoofer and center speaker. I was looking at Aperion 422/S8.

Most Cable TV appears not to use the surrounds even though the Denon display shows Dolby Digital.

Only movies appear to use the surrounds, and I would question what percent really use them to full effect.

If the program states 5.1. then it is available dependent upon your local service provider.  How well the networks mix 5.1 is a different debate.  As for 7.1, the only true sources for 7.1 are the new Dolby and DTS HD formats that are available on Blu-ray and HD-DVD discs.  It may take awhile for the studios to begin and get it right.  Most 7.1 today is a result of digital processing in your AVR.  You can certainly debatethe benefit of surrounds on network broadcasts, but the center is definitely worthwhile.

In addition to the 422/S8, also take a look at the 5 series. The new 533-T tower is a really sweet speaker.  A nice system would be the 533-T, 532-LR, 533-VAC, and the S-10, though it will set you back a few more $ than the 422.

I think Ken is right with taking a look at the 5 series......that's a sweet receiver you have there and as good as the 4's are the 5's will be a much better match