Sometimes I doubling with my Fishman Full Circle equipped URB and a basselines Hot Stack equipped Passive Jazz Bass. Since the Semour Duncan hum canceling design, my El bass has much less output than my URB, and need to add bass EQ. So I think to use a Sadowsky outboard preamp, It's a very nice preamp for el bass, has a mute switch for changing instrument without noise and has a bypass switch to get the URB sound without EQ and the buffered output. For my URB I never felt to need preamp before my amp. What do you think?