Guitar/music question...

I've picked up a couple cheap Fender 15w practice amps that have RCA inputs for a CD player (or really MP3, phone, anything).

I got them so guests could jam with if they were so inclined.

They are likely the kind that comes in the $150 starter set with a guitar, bag, pics, etc.

They sound pretty good, and the most I've paid is $25.

I've not used the RCA input and I don't know how you control the mix.