Hi,
I was wondering how much difference in sound quality between them? how about the feature? thanks.

There is zero difference in sound quality. Here is a list of things you get with the 3805 that the 3803 doesn't have or do:

• Dolby Pro Logic IIx
• Additional 10 watts per channel (8 ohms, 20 Hz-20 kHz, <.05%THD)
• Auto Setup & Parametric Room EQ
• Extended Bass Management Crossover Points (150/200/250Hz)
• DENON Link 3rd Edition (Super Audio CD & DVD-Audio) compatible digital input
• True 3 Source, 3 Zone functionality with discrete power, Source Select and volume control for each zone
• ALPHA 24 Processing Plus (AL24+) on all channels (not just the front speakers)
• EL backlighting pre-programmed/learning remote
• Two (2) assignable +12V triggers
  

No difference in sound quality. The 3805 has additional (PLIIx), but not better. If you can score a 3803 for $600-$700, go for it. You won't be disappointed. The only reason for the 3850 price premium is to have the latest/best.

AF, as Peter and Ray have pointed out there's no reason for there to be any difference in their basic sound quality since each is audibly transparent. Where there can be a difference is in applying the automatic equalization which the 3805 has and which can(only partially)correct for listening room problems.

What's up, John? Are you abandoning your auto-EQ position?
You have been such a proponent of that feature I thought you might have invented it.

Thank you all. I'll check it out on audiogon or something. Probably, Rotel is my next concern if my budget is not tight