Not sure if this is the right place to ask this question. I have a spider jam which I am delighted with but I would prefer a "warmer" sound. By "warmer" I mean less harsh (am I making any sense?) Anyway this is my question "can I replace the standard 12" speaker with a 15" speaker of the same output (ie 75W  8Ohm)? I know there are physical limitations due to the size of the combo cabinet, but apart from that is there any reason why a 15" speaker wouldn't work and would it damage the amp in any way? anyone out there tried this? thanks regards Mike.