X-Fi is a product, not an industry standard. His laptop is new and should be able to handle surround sound, any other hardware based functions like EAX won't be applied as the hardware isn't capable of running them.
Reduce the graphics settings, an x600 doesn't sound like a powerful card and San andreas is a poor console port that's not terribly forgiving on pc graphics cards. Sound might also be being processed by your cpu, ensuring no background programs are running should free it up a bit to help it out, though with a dual core i'd doubt this is the case.