I would suggest that you download the latest drivers from Creative for your X-Fi soundcard and see if that helps.
Heres a link to their support page...
http://us.creative.com/support/
Also...you might try turning down the sound acceleration a bit.
Oh..almost forgot...Are you playing SH 4 patched to v1.3?
If not...do so because that patch solved some of the very sound problems you describe, ( looping sounds,etc.)
Cheers!