Did you mean to say "HK AVR 340" instead of "Denon AVR 340?"
The 901 and 3805 are comparable - and somewhat dated
. You'd need to jump to the HK635 to come close to those. The 803 doesn't have the large power supply or caps as does the 901 and 3805. It does sport the newest gadgets in dealing with PC/Ipod/HD compatibility.
Other comparable AVR's (power/flexibility) would be the Yammie 2500, Pioneer 54TXi, Marantz 8400).
Check your impedance and spl ratings on your speakers. You may be fine with the newer Onkyo 803 or HK340. Most AVR's when set flat are pretty transparent. It's the internal PEQ/graphic eq, auto setup features, etc... that will make a difference when balancing out your room. Tweakability in an AVR is just as important as brute power.