How important is PC for CD vs Amp Pre

Are you using a power conditioner with an IEC plug? That is a good place for a power cord upgrade before most other places IMO.

The biggest bang I have obtained for my buck has been with source component PC upgrades. Without getting into the details, because ... well, quite frankly I don't think I understand it all, with PC upgrades I found a noticeable reduction in the digititus and glare associated with CD playback either from a dedicated CD player, or when used on a DVD player for CD playback. I found limited (tough call) benefit from PC upgrades on my pre and power amp. I BELIEVE that the quality of the power supplies on the different components to be the factor in what I observed/heard. YMMV. Good luck.

The biggest bang for me, in my experience, is making sure every cord in the system is decent - that is, no stock cords. I surmise that one of the reasons for this is the PC is trying to eliminate noise - therefore a decent cord everywhere is a better defence against noise than only one great PC in the system and lots of stock cords letting the gremlins in elsewhere. After that, I would think about selecting the best cord you can find for your source.