I ran my VH4S with an older RL Diezel cab and a new FL. Sounded brutal. But that's all I can say, also sounded brutal through just one cab. I don't think there'd be much phasing as the head would be supplying a fairly simultaneous signal to both cabs. Sure, if one was out 100ft and the other 6 ft, maybe something going on there, but otherwise, it would just sound like to cabs being powered.