Taking my univalve to practice tonight, its usually fine for volume. Got a different drummer today though. If I need to slave it into a poweramp, I presume I only need an instrument cable? Or does it need a speaker cable?
The benefit of avoiding the second preamp is that you don't get the gain/eq from the 2nd head. You are basically just increasing the volume of an already cranked head. That being said, going into the input may work for you...