Can't the Raspberry Pi run an AirPlay receiver via XBMC? It costs less, and can stream 1080p video. The 3.5mm jack for audio output isn't ideal, but it can also run audio over HDMI if you're set up for that.

TuneBridge definitely looks like a more consumer focused option, but for the price you could put RPs in a nice case with custom software and still make a profit.