Right, thought i'd post here. I did a search around some guitar forums, and the amount of BS just made my head hurt too much. Anyways, my mate has a marshall JCM900. On the back, at the impedence switch it is as follows : (4) 16 [-] 8 (the [-] is the switch). He currently has an 8 ohm 2x12, and is thinking of adding another 2x12 so he can have a 4x12 when he needs it, and a 2x12 when he doesnt. Going for a modular approach (he's quite bright for a guitar player). But anyways, he was asking me about impedences (I said he was bright for a guitar player ), and, i was wondering, but looking for some clarification. Would it just be a case of sticking the switch to "(4)16" and plugging the two cabs in so they were in parallel giving a 4 ohm load? Read some stuff on guitar forums claiming that no amps can handle 4 ohms, that you would want 16 ohms anyway as it sounds better. And the (4) is only there because it is possible to mod the amp to use a 4 ohm load. (which seems a bit wierd that they'd list it on the back when it cant do it). So, anyone know the score on these amps?