Help with Rega DAC set up

I'm finally off the digital fence. I've considered for awhile, a CDP upgrade/update or going to a DAC and using my Underwood 1+ modded Music Hall CDP as a transport.I just purchased a Rega DAC with Pangea adapter. I have a few questions before I set up thus DAC next week.

How well does this DAC respond to powercord changes?

My transport can output a coaxial or optical signal.Which one is better with this DAC? Any specific brand recommendation?

I also have the Pangea adapter. The cord does make a considerable difference. I have used several including Shunyata, Oyaide and PS Audio. I would use coax myself; some friends were over last Sunday and we tried several; they all sounded different. As with power cords which you prefer will depend on your system and your taste. I am using a Clearer Audio silver cable just now; have also used a silver Oyaide 510 and Van den Hul "The First Ultimate". Many standard ICs will work but not all; try what you have on hand. The 5 filter positions also have a significant effect; I use filter 5 most of the time but again tastes will vary. Good luck; it is a very good dac. I like the NOS approach I am considering getting a more expensive dac using this method.
The toslink sounds better... Glass optical.