Should work perfectly fine; neither of the headphones you've selected are terribly complicated to drive - the Q701s will appreciate a *bit* more power (we're talking 1mW-ish continuous; that's peanuts for most portables anymore, but consider that many headphones will use a tenth or hundredth of that for the same output).
The last post makes absolutely no sense - "impedance resonance"??? Perhaps you're trying to describe what Meier talks about here:
http://www.meier-audio.homepage.t-online.de/tipstricks.htm ??
Generally the reduction in voltage/power isn't a problem - the amplifier inside the receiver usually has enough gusto to overcome it (sure, it's inefficient - when you consider that, say, a Fiio E9 or CI Audio VHP-1 will use maybe a few watts at full volume driving a pair of cans, while something like a Yamaha RX-770 (it's an old stereo receiver) will draw around 30W, and something like a Denon AVR-4311 will pull down well over 100W (thank all those DSPs, not the amplifiers) for the same feat), and the FR variation may or may not be a problem (we won't get into damping factor beyond the explanation that it generally isn't worth bothering about); sure it can cause some anomalies, but it shouldn't fundamentally change the headphones.
Basically, the short and sweet is, yes it's quite good enough (and I'm not disagreeing with Meier). Inefficient (you're probably going to be using many of those DSP features though, so that's a plus!), but good enough.
As far as "24-bit DAC vs 16-bit DAC" - really does not matter unless you're playing back 24-bit material; are you? If not, who cares. If yes, then you want the 24-bit chip quite obviously (it's the only one that's compatible).
