AirPlay is always 44.1 going out. Worse, Apple TV will up convert this to 48k (and there are plenty of ways to do sample rate conversion badly). While messy, I did get my 8801 to play 96k ALC files in their native form using a DLNA server set to never transcode. Fortunately, the 8801 knows how to deal with ALC and FLAC. Not as convenient as AirPlay, of course.
Airplay may always be 44.1 except when converted by the ATV, but there's no doubt it sounds better streamed from a PC over an iPhone or iPad. How are your high res files playing on your network with a HTPC or HD plugged into your router?