Just got a 70s v4b, loving the heck out of it, but I want to get a 1x15 cab to add to my 4x10. The ampeg 4x10 is 4 ohms, but all the ampeg 1x15s I'm seeing are 8 ohms. How do I hook this up? In series, parallel, etc. The V4b has a ohm selector of 2, 4, or 8, what do I set this at? I've heard...