Is power cord upgrade now still necessary?

Not sure I understand what you are asking. But a power cable upgrade would possibly enhance the performance of the transport and since it is transport only, any improvements would be evident regardless of connection to the D/A.

I agree w/ Theo, and would like to add that a PC upgrade to the DAC will make a big(ger) difference -- regardless of how you connect the CDT to the DAC. Make sure you use a PC with 10AWG conductors like for an amp (I know -- don't ask, we can't figure out why!) Also, make sure any PC used w/ digital components has a floating shield to keep the cable from "broadcasting" digital RFI into the air.
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Power cords can improve anything with a motor like a turntable or CD motor as well as improving the sound of electronics in general. Make sure you get the AC polarity right.

Thanks for the replies. I agree that power cord upgrade can make huge difference with DAC. I upgraded my DAC power cord from Cardas Golden Ref to Nordost Valhalla and the difference is huge. And I am sure PC upgrade for CD transport will be nearly equally effective if I use normal digital (metal wire) interconnect. I just wonder if anyone who use ST glass digital interconnect has CD transport PC upgrade experience?
I swapped Valhalla PC from DAC to CD transport (with CARDAS Golden Ref PC), the sound will not be as good as before. I am not sure if the reason has anything to do with ST glass cable. When I use Transparent Ref digital cable, the difference seemed not that much by swapping the PC between CD transport and DAC.
I use Theta David transport and Theta Gen Va 24/96 DAC. The are quite old, but I like their sound.
Thanks!