Hello, I'm looking into a headphone amp that can take at least 3 different inputs, each with their own level. Me, my guitarist and keyboardist all want to run into this to make dorm room pracices much easier. Obviously we need to be able to send 3 headphones out of it (but that can probably be fixed with a simple 1 to 3 out adapter). Any units like this? When they say "4 channel headphone amp" does 4 channels refer to inputs or outputs? Thanks