Upgrade my CD player or buy a DAC?

I cannot decide wether I would be better off buying a dedicated CD player or a DAC and use my current player as a Transport. I am currently using a Yamaha BD-S2900 as my CD/DVD player. I use my system almost exclusively for 2-channel audio, mostly Folk, Rock, and Jazz. My current setup:

Vandersteen 2CE Sigs
McCormack RLD-1 Preamp
Sunfire 5x200 running Biamp
Yamaha BDS-2900
Apple G5 for digital music
Audioquest King Cobra Interconnects
Audioquest Type-8 Speaker Wire

I have a budget of up to $600, let me know if you have any advice.
At that price point I would get a Musical Fidelity V-DAC and a decent digital cable.
Also consider the Moon 100D. Whichever digital cable you buy (I seem to like cryo'd OCC copper cables myself), make sure it is 1.5 meters long.
There are a couple of good arguments for going with a separate DAC. One is that DAC technology is changing rapidly and having the flexibility to upgrade in the future may be an advantage. You'd also have the option of going to a better transport when you can afford it.

The other is that an external DAC would let you have multiple digital inputs. There are players that have digital inputs but probably not within your budget.

And I'd second Tobias recommendation of the Simaudio Moon 100D.
i would suggest to save your money until you can get the wyred 4 sound dac1 or dac2. it all depends if you want to upgrade to something much better in the future (and lose money on a cheaper purchase) or buy something top notch and grow into it with future upgrades from your other equipment.
The answer to your question is a no brainer. Go with the seperate DAC! If I were you, I would save a little bit longer and get a used (from this site), Benchmark DAC. It will be the best investment you have ever made. Read the reviews. Class A in Stereophile and has been since its introduction. It's also a headphone amp. It can be used as a preamp. It has both single ended and balanced outputs. Absolute bargain. I have seen them on this site for less than $600.
I think that most would agree that the DAC has a more significant impact on sound quality than does a transport, especially at your price point.

Test 1: Connect your CD player in parallel through the DAC and directly to the system for an A/B comparison of sound quality.

Test 2: Connect a 2nd CD player to the DAC using an identical CD and do the same A/B comparison.

I suspect that you'll confirm that the DAC is a better upgrade.

Also, a DAC can be used with multiple pieces of equipment. I do not believe that you could get a new CD player that can double as a DAC for your budget.
I second Griffithds's recommendation: Benchmark DAC1. If you're patient, you can find one second-hand for $600. If you don't like it, you can sell it on without a problem. It's a fantastic piece of equipment.
Thanks for all the input! I was leaning towards a DAC and I have heard good things about the Benchmark DAC1. Are there any other DAC's you would recommend? The Musichall 25.3 also caught my eye.
The Benchmark DAC, which I have auditioned a fair number of times, has a large
following for good reason: it digs out detail like no other I have heard. It is
impressive and you may love it. My own preference ultimately went to a DAC
which I felt provided detail, yes, but also a special sense of the overall flow of the
music. Both the trees _and_ the forest: I hope I may use the analogy without
appearing to denigrate the Benchmark, which I repeat is an extraordinary DAC. It
may be just right for you.
the benchmark was way too cool sounding to me, almost fatiguing. i have a music hall in second system that has an upgraded tube and i prefer that over the benchmark. the wyred 4 sound dacs are much better sounding that both these units IMO. i thought it equaled if not bettered the ayre dac which is a great dac but limited in input.
Another option is to consider a modified player that has a good 24 or 32 bit dac in place. There are many that come up on this site. IMHO, it does come down to cost vs benefits. I Had a M-1 Musical Fidelity DAC($700)that blew me away till I heard what a 32 bit DAC can do.