I don't have any experience in the P4T533, I've an audigy platinum. But onboard soundchips usually has more cpu load than a hercules muse 5.1 or an audigy.
If you want to pay extra, I would buy an audigy player or a hercules muse 5.1.
I never liked the onboard sound (limited functions).
The fastest cpu of today will be slow on the same day next year.