I have a Denon 1804, it is pretty good in 2 channel. But it will really depend on your speakers. I read in a report on that receiver that it is closer to 100 watts a channel in stereo mode, it is rated at 90.
Measured by Home Cinema Choice (all numbers into 8ohm):
Denon AVR1804: 2ch: 2*110W 5ch: 5*35W
Marantz SR4400: 2ch: 2*110W 5ch: 5*85W
Onkyo TX-SR501E: 2ch: 2*80W 5ch: 5*35W
Sony STR-DB790 (=DA1000ES in US): 2ch: 2*96W 5ch: 5*65W
Yamaha DSP-AX640SE: 2ch: 2*105W 5ch: 5*39W
So it seems that Denon, Onkyo and Yamaha all have very underpowered power supplies and cant perform as well as Sony or Marantz with all channels driven. For also good multichannel power check H/K AVR130/230 and NAD T742.