I think he wants a total of 3 zones. If he wants 4 zones, still no problem, plus we are probably going to do a video/audio zone via HDMI. So a 7.1 channel DAC is probably more than he needs.
The price on the ASUS seems perfect to me. Add in a few 3.5mm to RCA female adapters and we should be all set. I'm anticipating runs of up to 80 - 100 feet. With shielded RCAs I don't *think* that will be a problem. I've never had any attenuation of signal in RCAs before, though this would be about double the longest run I've never made. Hopefully balanced is not necessary, because that would probably make the project take another direction: It's just too much work (money) to unbalance it at the other end, etc.
Ideally you want an amp with a balanced input, so no need to unbalance, but I know what you mean (amps with balanced inputs aren't always in wide supply, although behringer makes some nice and cheap ones). I haven't done cable runs that long, but with good shielded cables you should be able to deal with much of the mischief. Lord help you if you have a ground loop though
Is this ASUS a good DAC? I don't mean in an audiophile sense, but rather in a basic "hifi sense". Does it have nearly zero noise? Does it sound "just fine" ? We definitely don't want any weirdness, noise, buggy drivers, or anything like that. The budget can be extended past the price of the ASUS to insure hassle-free hifi performance.
Here's what I will say: it's very, very good for the price, and I can't think of another multichannel sound card (internal or external) at that price range that I would recommend in front of it (for Windows use). Some of Asus internal cards have allegedly better specs, but do not actually measure better in practice IME. No device has "zero noise," but the rated THD+N is 0.0006% (i.e. -104dB). You can see a tear down and independent measurements here:
http://www.diyaudio.com/forums/pc-based/268678-asus-xonar-u7-usb-soundcard-review.html, which show a higher noise profile in practice (which is universally the case). My own measurements were closer to Asus's than the teardown's, but I wasn't using a loopback/rightmark methodology, so that's to be expected (rightmark measurements tend to exaggerate noise because they necessarily add the input noise to the output noise).
I have never heard audible noise or flakiness from the U7 in a windows environment, and I have recommended it to budget conscious friends. But if you really want rock solid performance, I would recommend looking into the more expensive pro audio interfaces. Matt and Hendrik both run Focusrite 18i20's, which are highly regarded. I run a Steinberg UR824 and have never heard so much as a peep from it in years of operation. Both those interfaces are significantly more expensive though (although they happily have balanced outputs
)
The best thing to do if in doubt about the U7 is to buy one from a place with a generous return policy and test and see what you think in practice. Amazon tends to have a fairly generous return policy as long as you move quickly.
DISCLAIMER: Most of U7 testing was with Windows 7 and 8.1; I haven't done extensive testing in windows 10 (although it appears to work fine based on a quick test, I haven't done daily driver use in Windows 10, so can't comment firsthand on long-term stability).
Oh, the target computer: I believe it will be running Windows 7, 8, or 10. It would be nice if the DAC was also Mac compatible for future use, but most DACs seem to be easily plug and play (I hate that term!) with OS X, so that's probably a non-issue.
FYI do not count on an interface being Mac capable if it does not advertise itself that way. Especially when you get into multi-channel interfaces support on non-windows platforms gets increasingly spotty, or requires manufacturer drivers. Especially insidious is that a friend of mine has run into devices that appear to "just work" when plugged into Macs, but only work in reduced capacity (not all channels available, etc.). So if future Mac use is part of your build out, make sure the device actually supports OSX.
Of note, my understanding is that the base model Asus U7 doesn't fully work with OSX (plug and play, but many features not addressable), but the "echelon edition" of the U7 does work? I don't know as I don't use Macs, but I'd advise investigating thoroughly. So caveat emptor!
EDIT: from the amazon comment threads it appears that the U7 is not officially supported on OSX and certain functions won't work, but it's not clear exactly what (other than the volume knob). It sounds like the OSX support is about like the Linux support, which is not that suprising given that it's the base UAC2 mode that the thing is likely running in on both OSX and Linux.