C0deHunter wrote on Today, 06:05:

If I get an OEM version of the X-Fi Titanium (with 16MB X-RAM), which features would I miss compared to the Fatal1ty version?

Dolby Digital encoding might not work on some OEM X-Fi cards, if that matters to you. Otherwise, there shouldn't be much difference.

C0deHunter wrote on Today, 06:05:

I am planning to play Prey, Quake 4, Doom 3, Battlefield 2, etc.

Those games make good use of X-RAM, and can store some audio files there for faster access, but that won't impact your listening experience. X-RAM was supposed to improve performance back in the day, when single-core CPUs were struggling with some demanding games and mechanical hard drives were slow, but how much that helped is debatable. If you use a Core2 CPU or better in your WinXP rig, as well as an SSD, it likely won't matter.