i want to record some of my stuff but im not sure how i should go about it. i have a game theater xp which has RCA, 1/8 stereo, optical digital, coaxil digital, and a mic input (1/4 not xlr). my question is what can i use to cleanly record a bass or guitar with those inputs?

i have heard of a direct box but i cant find any info on what exactly it does. it seems they allow direct line recording which would be fine but i dont quite understand what outputs they feature. i would prefer not to record by miking my amp so im open to any other suggestion. keep in mind i cannot afford to buy a sound card dedicated to recording which is overkill anyway.

what im looking for idealy is an add on solution that will complement the gear i already have. the less expensive the better since im not making some multi million dollar platinum hit, im just practicing.