Best DAC for CD redbook playback from a PS Audio Perfectwave transport

I just purchased a PS Audio PWT and will use it to listen to redbook CDs. I've read that the best playback is with an I2S hdmi cable. So, a suitable dac would be one with an I2S input, such as either a Wyred4Sound dac or a PS Audio PWD. But, if it's just for redbook CD playback, can I suffice with an older MK1 version or do the updated versions (which I presume are primarily geared toward improving computer based systems) also significantly improve CD SQ? Again, it's just for CD playback.
You will get your best sound with any format using the IeS bus.  
Thanks stereo5. Yes, I've read that I2S is the best. But, considering it's only for CD redbook, is it worth splashing out on the latest version dac with and I2S input (even a PS Audio Directstream), or is it wasted money? (e.g. just buy an older version used)
For what it's worth, I'm so happy with my PWD II that I have no yearning for a Directstream.  I'm using the Bridge II with fantastic sonic results, but the Perfectwave Transport hooked up by I2S should be just as good.
Thanks cymbop. Yes, it seems as if the PWD II is the way to go. Directstream, I'm sure is better, but for the money, PWD II feels right. Anyone have any experience with hdmi cables?
Okay, now it gets more interesting. Metrum DAC (without the I2S connection) vs PSA PWD MkII? Anyone know (for CD playback)?
I have the PS Audio PerfectWave transport and DirectStream DAC, with a PS Audion I2S (HDMI) cable, and it’s the best combination I’ve auditioned.

I have had the DirectStream DAC now for about 18 months and am really impressed with the detail it extracts from CDs, even better when I added the transport (my latest acquisition).  The great thing about that DAC (besides the quality) is that updates are made available on a fairly frequent basis, each one of them has improved the performance.  Thoroughly happy with both products.

On the advice of one of my audio buddies (retired electrical engineer), I also purchased a PS Audio P10 power plant, "power regenerator".  When I added the P10, I noticed an immediate improvement in the performance of the DAC.
The PWT is an excellent CD transport and will work well with any high quality DAC IMO. I use the PWT with a Yamamoto DAC and have heard it used with an Aesthetic Pandora  DAC as well. In both cases the sound quality was terrific via rca input /cables. 

Thanks all thus far. In the meantime, I found the following from a review in Home Theater by Brian Kahn "I found the Bridge to provide the best sound, with the PerfectWave Transport via I2S a close second." That's reassuring.
Thanks all. Just splurged (it was my birthday) because I got a good price on a PS Audio DSD Junior + Wire World Platinum hdmi cable. Will post results after burn-in.
Best DAC for CD redbook playback

Get the best you can afford that uses R2R Ladder Multibit dac conversion, as it does it "Bit Perfect" for Redbook (PCM)

Stay away from all Delta Sigma based dacs that are for DSD or otherwise, as they only give a facsimile of Redbook (PCM) conversion.

Quote: " When a PCM file is played on a DSD or Bit Stream converter, the DAC chip has to convert the PCM to DSD in real time. This is one of the major reasons people claim DSD sounds better than PCM, when in fact, it is just that the chip in most modern single-bit DACs do a poor job of decoding PCM."

Cheers George

This review by Robert Deutsch answered all of my questions about CD playback with a PS Audio PWT. The answer to my original question, is yes, it is worth it to splash for the latest DAC instead of the older MkI version. Thanks all, mission accomplished.
I have to agree with Robert Deutsch in his assessment of the PWT.  It has consistently outperformed the transport sections of CD players in direct comparison I've heard.  It is a top tier transport for Redbook CD sound quality. 
Thanks Charles,

PS Audio told me that they were so confident about the DSD Junior that review units were sent out simultaneously with the product launch, instead of before launching. The Junior was launched in February and it takes a few months to review a product so we should have reviews by the summer.
I had the perfect wave mkII and upgraded to the Directstream. It's almost night and day. The DSD is the first time I've heard a DAC that sounds (almost) like analog. 
This is easy - the very best you can get is the Stahltek Vekian, or Opus, or Opus Prime DACs.  Unfortunately, all are megabuck.  But you can rarely pick up a used Stahltek for something in the vicinity of 10K. The Aria is more affordable and give most of the performance, but have never seen one on the used market. 

Ordered a PWT yesterday with a DS Junior and should (hopefully) get it next week. Can't wait :-)))))))))))