Everyone, thanks for all these suggestions.
Believe it or not, a few hours before jarcher posted his recco for a Mac Mini, that's basically what I decided the route I was gonna go. Regardless of how I transport music to my system, I got thinking that it makes sense to have a dedicated music server just to free up my laptop from that role, with the added benefit that I can use it for movies too if I decide at some point that I want a full fledged HTPC. I found an early 2009 model that has an 802.11n airport extreme card for $300, and I'm thinking that I'll pick it up, load Linux onto it, and then experiment with running XBMC together with XMBC Remote on my iphone. The price is right, it offers me some additional capability that I believe I'll find useful beyond my primary goal of hi-res transport, and there are a ton of software choices if I decide I'm not happy with the Linux/XMBC setup, several of which you all have mentioned in your posts.
It's curious the reports that jarcher mentioned of digital output via USB/SPIDF coverter sounding better than optical. I'll read up on it, and maybe I'll get a converter eventually, but for now I'll go with optical.
Thanks again for all of this input. It was really helpful. I'll post again when I finally get the Mini setup and integrated into my system. (I expect it will take me a little while.)
