What does the switch actually do? The Mesa literature says that it reduce the current at 2 ohm to protect the amp from over-heating, while still generating full power of 900 watt. But how is that accomplished? Does anybody know? I supposed it's totally different from (tube) amps with an output transformer and different tap, right? Would I get reduced power when switch to 2 ohm, but run a 4 ohm load? I tried running the M9 with a 4 ohm load, in both 2 ohm and 4 ohm switch position, but it does not seems to affect the volume level at all. Any ill effect if I just leave the switch in 2 ohm position all the time I wonder why there isn't more amps operating the same way to provide 2 ohm capability.