I have not had the Sonar, so cannot somment on that.
However, I am a musician/producer(ableton,reason and cubase), developer and gamer, and I run Vista 64 (o/s important when choosing sound card) and love my X-Fi Xtreme Gamer.
Signal/Noise ratio is excellent, it has everything I could possibly need and the software package is great (really, the best I have seen).
I don't know about surround etc, but the Xtreme GAmer is everything I need, and quite possibly everything you need too.
Bear in mind that the Creative cards are the specified cards for gaming (EAX etc) and the decision should come a little easier