Audiophile grade computer?

[rando]

1. Any computer used as a base upon which to effect the requisite number of changes you implement for your own listening pleasure.  Whether that is choosing to use what you have, trying everything on the market, or conducting a mad science project without end.
2. Partial answer is all that is possible.  Adding a second device with considerably larger and better implemented handling of power will have an effect.  Not necessarily fitting the loosely structured question as presented.  The amount of noise present from your home's electrical source is certainly a consideration.  We live in an age where there are countless solutions to problems you may not have or have any need to solve.  Half the fun is figuring out if the addition of them fixes a problem you actually have or do anything at all.  Common sense and experimenting will offer much in the way of wisdom.
3. Cable construction makes a bigger difference at either end of the spectrum where atypical methods are most likely to be encountered.  Using a good quality $10 USB cable will take you quite far in price and SQ.  You may have to step up to a custom made one if your needs expand beyond straight connectors in standard lengths etc.  Cable debates are anathema, though I'd say most would take this in the context offered.