That is interesting as our guitarist's sister is J'anna Jacoby! She says he's great mind you J'anna is a looker and you know what rod is like with the ladies!
Oh and you get "RTA" real time analysers, so you can see which eq channel is feeding back on the screen and cut just the problem one, 31 band eq on each output all separate so you can just pull the bugger that is causing it which doesn't really hurt the mix compared to say a 7 band or a low/mid/high.
Well it can help to get you in the ball park, I normally look for a similar venue from my previous gigs, wooden stage, low ceiling, hard floor, marquee etcetcetc.
If it's a regular venue you play at then you'll have all the settings saved from last time you played there, set it up the same as last time and use the same kit and mics and you only really need to make sure everything works at sound check, a budget version for a typical desk with knobs is to take photos of the knobs after each gig.
Sounds like you got it easy if he goes to the bar 'after' sound check, most would do the annoying rattling the kit thing for ages then disappear just when you need them for the only five minute slot you are allowed to sound check!
I'm just thinking without the cone the motor would move freely and produce no sound but would have the variable characteristics of a speaker rather than a fixed value resistor.
I've never had any amp flat out with a single cab anyway, either I had enough volume or the single cab farted out before, I'd imagine that is the case for most of us?
If your amp is matched to your full setup of two speakers or more then ideally when it's only running one of the two cabs then it's only putting out around half of its oompf.