Splinter Cell Xbox problems

Lately I've been playing Splinter Cell on the Xbox and whenever a loud noise comes on, like having a grenade go off near me or someone shooting a gun near me, the surround system turns off. I have an RCA HTIB, 500 watt, 5.1 system. Does anybody have this problem?

BTW, I'm thinking of upgrading the basic configuration I have. I'm thinking about getting a powered sub and new speakers, but I'm a complete noob on the subject, hence the HTIB. Any suggestions?