Is power cord upgrade now still necessary?

I just changed my digital interconnect to a ST glass optical cable and the sound is great.
Do I still need to upgrade the power cord for my CD transport? If the improvement from power cord is something electronic, it will not pass through the glass optical cable (but can pass to the next stage by metal wire).
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.
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.
Zdeng -- using coax digital (metal) cable between your tranport and DAC would (at most) tie the two units' grounds together (and possibly not even that, depending how Theta designed the circuitry.)

So if you don't have hum problems, I wouldn't worry about it. As for sonics, I've used ST for 15 years because, although my Wadia WT2000 CDT had all kinds of output choices, my Wadia 64.4 DAC had only a single ST input! I did however begin upgrading my ST cables a couple of years ago, with just minor improvement, UNTIL I finally sprung for an Aural Symphonics Optimism 2 ST cable ($950 msrp -- I was lucky enough to get one used ;--) What a huge difference! Really, it was like a $20k (at today's prices) component upgrade!

I've since upgraded my DAC to a Wadia 27, so I have all possible types of input/output choices, but I know I'll never part w/ my Optimism 2. It's just too good -- in fact Aural Symphonics now makes a 3 cable ST set for the Meitner CDT/DAC ($3000!) which a lot of people are raving about. I guess what I'm saying is keep your Theta equipment, it's great stuff lacking only SACD (not important to me!) and see if you can score an Optimism 2 someday, you'll be very impressed.

As for PCs, any good PC (meaning with conductors 14 AWG or larger) will do for the transport IMO. I use a 10 AWG Purist Venustas on my DAC which made an audible improvement.

Thanks so much for your kind reply. I happened to use Meitner ST cable. There are 3 of them in different color, supplied with a EMM CDSD & DCC2 combo. I am not sure if they are made by Aural because I can not find "Aural" trade mark printed on the cable (nor the EMM trade mark). This is my first time to use ST cable so I do not know if it is better than other ST or not. Do you find any coax digital cable which is nearly as good as your ST in your system?

Anyway, here I find THE right person to ask my question: When using ST cable, do you think upgrade CDT PC can be as effective as when using conventional digital cable? What PC do you use for your CDT? What is your upgrade experience?

Many thanks
Zdeng, you can see the emm Optimism at:

I don't know what the "stock" emm ST cables look like. I know that before the emm Optimism, people who owned emm preferred coax to the stock emm ST, but now prefer the emm Optimism ST over the coax.

I haven't had a reason to A-B my single Optimism ST vs. coax, because a coax cable that would be fair competition (like a Purist Dominus or other high-end digital cable) would cost too much. So that will never happen ;--)

As for PC and digital interconnect combination, I don't think there is any interaction between them. They are separate issues/upgrades.

I do think the PC you use for the DAC is more important than the PC used on the CDT. The DAC should be 10 AWG and shielded -- I use a 10 AWG Purist Venustas. A Dominus would be even better but twice as much money ($900 used!)

For the CDT, any shielded PC, 14 AWG or larger (12 AWG or even 10 AWG) would be fine. It doesn't have to be expensive. I have some extra XLO Ref 2 (12 AWG, shielded) I'm selling for $100 which will work fine for the CDT.