modest DAC for iMAC+iTunes?

I have a new iMAC which I currently connect to a vintage Marantz 2250B for my bedroom system. We use it for iTunes, playing CDs, and streaming internet radio. I use analog cables with RCA jacks.

I would like to try a DAC for the best sonic quality. I think I can get a lower noise floor. Can I get something for < $200 that would work well or are we talking more $$?

Not sure what the jitter performance is of the MAC digital output.

Any recommendations?

I own the Musical Fidelity VDAC and am very happy with it, no desire to "upgrade". Can be had used around $200. You may also want to check into the new Jolida DAC, only runs a little over $100. Budget DACs have become very good over the last few years, with a budget of $200-300 you can do very well.
Scott Nixon Chibi
Check out Nuforce Udac, USB in only though. Can't be beat for the money ($99), considering it uses the new Sabre dac chip.
HRT Music Streamer II ??? Anybody have any thoughts ?
I'm getting great sound running itunes via my PC into a Music Streamer+ in my secondary system. No complaints at all. The price on the original Music Streamer+ has dropped to $189 BTW.