Hi, Cactustone. I'm a guitar player and know nothing about the U5, but you should be aware that the SF-2 includes a preamp that can be set at 0, +10dB, or +20dB. It comes from the factory set at +10dB and can be changed with an internal jumper switch. I've put an SF-2 into a guitar combo, an F2-B preamp, and a bass combo with no problem. I might start out hooking it up set at 0dB and see how it sounds.
Bill, tgo