If you're just looking for improvement on your CD player, I'd say it's not worth it. I don't think you can get any significant improvement putting a $500 DAC on your approximately $350 NAD CD player.
For me, to use a DAC on my Cambridge Audio 650C (bought for $500), to get any significant improvements would've cost me at least $1800 new (
Simaudio Moon 300D), plus the money for a good S/PDIF interconnect. I tried the
Moon 100D ($600) as well as the
Cambridge Audio DacMagic, and neither delivered anything close to significant differences. For the two less expensive DACs, if it was a blind test, I would've offered maybe $75 for the improvements I heard.
Unless your CD player is terrible, or you know of a DAC for $500 that outperforms the $1800 Moon 300D, save your money for something that actually makes a difference.
If, however, you just want access to other formats from other sources (e.g., audio from a computer), then perhaps the Cambridge Audio DacMagic would justify itself for you (whichever model you choose). You should be able to find one of those under $500.
I got more out of my CD player from a
LessLoss DFPC Signature (power cord @ $1149) than I did from the $1800 Moon 300D.
At the time of these auditions, the rest of my 2-channel setup looked like this:
Focal 816V (floorstanding loudspeakers)
Kimber 4TC (loudspeaker cable)
Yamaha RX-A3010 (amp)
Kimber PBJ (interconnect)
Cambridge Audio 650C (CD player)
2 LessLoss DFPC Originals (power cords: 1 on source; 1 on amp)
