I have two heads, a DSL-50 and a Peavey Classic 30 that I run into a single Marshall 4X12. Every time I want to switch from one head to the other, I have to switch the speaker output cord to the other head. Is there a way I can have an A/B box that will switch from one head to the other and run them both into the single cabinet? Does such a product already exist, or would something need to be custom built? Thanks in advance!