I'm not sure how this all got cloudy. It was obvious to me that @baddarryl was asking about a larger/louder cab to run INSTEAD of the Scout, not WITH it? Maybe we speak the same language or something.
As for that question, you're in luck. One of my favorite attributes of the Walkabout head is that it really does get along with pretty much any cab you throw under it. I have run mine with an Epifani UL410, an Ampeg 610, and a couple dozen provided backline cabs (including several Ampeg fridge cabs). It works with ALL of them. My main setup for years has been the 15" combo with a 15" matching Scout cab under it though. Holy crap. That's a warm, loud tone machine. But, yeah, it'll play nicely with any big honkin cab you like as a standalone.