Sounds a little strange to me,but 3 V-4's could run 9 - 4x12's cabs as long as they were 8 ohms.The Ampeg's impeadance switch goes down to 2 ohms,and the load would be 2.6 ohms / head.I don't want to guess as to how they've got the "slave" amp hooked up,I think the Ampeg rig would be fine as is.Be careful,Mel.