what you are describing sounds like a recipe for disaster. if the band is playing amplified electric instruments in a smallish room, you will likely only get a big pile of mud on your recording, and it wont matter what kind of mics or other equipment you use. the only way i ever found to record rehearsals was when we moved to a stereo PA system and started running everything into the PA direct. we used no external guitar amp or bass amp - we used a rockman bass box and some funky gallien-kruger guitar box - synths straight in, vocals into processor into PA, and i put a pair of overheads on the drums and mixed them with the output of the PA system. that setup worked pretty well for us to listen to our parts and overall balance. you can learn some valuable things from critical listening of your material that way. btw, we played several gigs using that stereo setup and it was damn convenient (all our balances were preset, and the bass player and guitar player were not always sneaaking back turning up their amp just a little more) and the audience loved the stereo effects we laid on them. good luck.