DAC recommendation for an entry level system


I would like to add an apple TV a Logitech Squeezebox Touch and a Dune HD Prime 3.0 blu-ray player to my system which consist of NAD C375BEE Integrated amp, Rega P3 24 and Revel Concerta F12 speakers and would like to know if anyone can recommend a DAC. I have my music collection ripped to FLAC and Apple Lossless on my server. I can go up to $600 and I'm willing to buy used. TIA
samaritano69
Micromega MyDAC: Asynchronous USB/Toslink/Coax 24-bit/192 Khz DAC for just $369. Check out the reviews linked from the "Reviews" tab. TAS was ecstatic about this unit.
Spotify does indeed stream at 320kbps, even through a Sonos system (as I am doing)

http://www.sonos.com/support/help/3.4/en/Sonos_User_Guide/Chap07_new/Spotify.htm