Not really sure what I need - DAC help

[TheNewGuy8]

SO here's my setup:

Macbook Pro --> (18" stereo jack to RCA) --> Marantz 2270 Receiver (vintage solid state amp, before integrated circuits, i.e. more of a tube feel) --> the output is either to a pair of Kef iQ1 bookshelf speakers, or to a headphone jack.

Now what I'm curious about is the role a DAC would play. I assume my MBP would connect via USB to the DAC, and then the DAC would ouput into the Marantz receiver?

I found an old M-Audio Audiophile USB DAC, and have used it (and noticed some definite improvement in SQ) but the problem is that it draws a consistent 30% CPU load. I can't figure out why. I'm running 10.5, and I assume it's just an old driver issue (even though I have the newest drivers). Should there be any CPU drain on a DAC?

Anyway - what would you all suggest? Since I'm using the Marantz I don't really need a headphone amp. I just use the headphone jack on the Marantz. Right now I'm using a pair of vintage AKG K141's (the 4-600 ohm silver variety). I've also got a Stax setup coming (SR Lambdas with an SRD-X amp).

So what sort of DAC would I benefit from?

THANKS!!

 

[cconnaker]

This CPU drain is very abnormal. Do you have any other devices connected to the same USB Bus?

 

[TheNewGuy8]

wow! Yes, the DAC is plugged into a USB hub with 3 or 4 other devices.

After reading your comment I unplugged it from the hub and plugged it directly into my computer. Bingo! No more CPU drain.

Why on earth was that going on?

OK - that said. How is the quality of the M-Audio Audiophile USB compared to some of the others?