What Clockworks meant was if you manually turn on the Amp within a sequence the smart state will still think it's off - so when you switch to an activity that includes the amp it will try to turn the amp on. If the amp uses a power toggle it will cause the amp to turn off instead of turning on.

There is another problem just using a sequence to turn on the amp and not using separate activities - volume control. If the amp is not part of the current activity you can't map the volume buttons to it.

Using 2 activities would automatically handle changing the volume control as well as keeping the smart state status of the amp up to date. Switching activities is only one or two button presses so it's not a big deal.