The Denon x1700 is rated at 80 watts @ 8 Ohms, 20hz - 20Khz, 0.08% THD, 2 channels driven. All channels driven, this amp should be doing around 55 to 60w. As I said earlier, I have heard this receiver and for listening at the levels specified by you, this should be more than enough.Cheers for that.
Funnily, as someone who found musical bliss with a 3W amplifier, i find even 50W to be more than enough power for most speakers. But point taken that 50W in an AVR is not the same as 50W in a 2-ch amplifier or integrated: there does seem to a lot of fudging going on with the specs when it comes to receivers. And i tend to be very sensitive to clipping/distortion, so this is a timely reminder to not be so blase about power with the AVR as i am with music amps.
Unlike a two channel amp, an AVR has the ability to set the crossovers to the speakers and let the Sub handle the difficult to drive frequencies. Get a decent sub and a good center channel and you should be quite happy with the power section of an AVR like the Denon x1700 at the levels that you listen to.