If you want to use a Speakon cable with a GK head and a non-GK cab, you MUST use a regular Speakon cable, NOT the GK cable that came with the head. Your problem is exactly as stated before, the bi-amp outputs are both being fed to the drivers, which is not good for the head. Seeing as how the sub amp is much stronger than the tweeter amp, you run the risk of toasting your tweeter amp and possibly damaging the power amp. It sounds to me like you should sell that Avatar cab and stick with the GK at this point anyways. Avatars go pretty fast on TB.