I guess you have ruled-out the possibility of a small HTPC or a Mac Mini. To play music I use a Mac Mini running iTunes, chiefly controlled from my iPhone, playing though an external DAC. I feel its tiny form factor leaves a very unintrusive footprint on my AV cabinet, even if the aluminium housing doesn't exactly gel will the rest of my hifi which is all black. But if you go with a Mac Mini, ideally you'd need to find something to bulk-transcode all your FLACs to ALACs. Macs don't really like FLACs much. (More accurately, the standard software they come with doesn't like FLACs, not the Mac hardware itself.)