PS Audio P300 or Cardas Golden Reference?

I would normally say go with the Cardas GR as I have my system wired with them. But one set really won't give you the noticeable improvemant that a cleaner power will. I would start with the power and then add the Cardas GRs as budget permits. One positive about the Cardas GR's is that here on AG they seem to hold thier value. One other suggestion is conatct the Cable Company about their Cable lending Library. That was how I narrowed it down to the GR's for my system. Try a few brands and models and see if you hear the obvious choice for your system.

What about the Cast connections between preamp and amp? I've hear that Nordost now makes a Cast cable that is very good, why not take advantage of potentially better technology if you have the opportunity?

The KCR and FPB600 are not cast ready!

My experience has been that improvements to power delivery are more noticeable than improvements on any other cabling. YMMV though.

It all matters and can frequently create a sonic maelstrom from which one may find it hard to escape. Use the cable companies loaner program or borrow from a dealer for an in home trial for any changes...it's the only wat to be sure!