With a pretty trivial driver hack you can get a GTX 980ti to work in windows XP:
https://mattpilz.com/windows-xp-drivers-nvidi … 980-ti-titan-x/
The GTX 960 is officially supported. For pure XP machine, I think the GTS 250 and the HD 4850 offer the best value, but that is all relative to what era of XP games you are trying to play.
As for Audio, you want the latest iteration of the creative chip. Last time I was looking, the X-Fi extreme gamer SB0770 and the X-Fi Xtreme Music SB0670 are the easiest to find. The "best" sound card for windows XP is the X-Fi Xtreme HD PCIE model, but most of the features on that card probably aren't that relevant to you, and it usually goes for around 200$ (it supports TSX and some later Doby standards).
https://en.wikipedia.org/wiki/E-mu_20K