Biamping is when you use a crossover to split frequencies, probably not what you are going to do, its a kind of specific term. dual amping is great though, can use a full on guitar rig, just cut the low end from it, guitar speakers tend to sound better with a driven guitar head, as they contribute to the tone. don't assume just because the 18 is big that it has lots of lows. Once you ahve the guitar rig filling in your mids and highs, yo can go a bit silly with the ls and use PA subs and suchlike. The Barefaced Dubster is kind of ideal for this sort of shenanigans.