Hey millarcarbon & caphill for your detailed replies.
Firstly I must say that I am extremely happy with the audio quality achieved through my Denon AVR and B&W speakers. It sounds amazing, truly fantastic in every way, soundstage, treble, base, fullness. etc. not boasting and also anecdotal I know, but I have had audio engineers and sound producers come listen and express how good they think it sounds. I have also had many hi-fi enthusiasts with McIntosh or Krell amps etc comment on the great sound. In fact I have auditioned many very expensive ($5,000 -$80,000) systems with separates over the years, and found the sound of my setup to be very good overall. (I know that this is all anecdotal, but I can only tell you my personal experience!) However, I am not unhappy in any way with the sound, I was just wondering IF it would be worthwhile 'Tweaking' things with a pre-amp or dedicated stereo amp. I like to experiment and try new things so was just curious whether a pre-amp could potentially improve the system and in the technical reasons why some would argue that AVR's are inferior. I respect your information and opinions, and sincerely wish you could hear for yourselves :).