Okay, I understand the fundamentals of figuring out impedance when it comes to using multiple cabinets and how those cabinets are connected to the head. My question is more in terms of drawbacks to running at various impedances. I've got a SWR Bass 350 head, capable of running at 8, 4, and 2 Ohms. (at 240, 350, and 450 watts, respectively) I'm going to buy a 4x10 cab for it and was thinking that I ought to go for a 4 Ohm cab so that I can get decent power output from it when played on its own. But should I want to add another cab to it, it would make it run at either 2 Ohms, parallel or 8 Ohms, series. Will running it at 2 Ohms cause wear issues with the head? I mean, will it shorten the effective life of the head, or have any other drawbacks in spite of the fact that the head is rated to handle cabinets at 2 Ohms? Thanks in advance . . .