With the accuracy of clip on tuners such as the Snark I see no point in adding one to an amp.
I find such threads as this a tad bizarre. There are not many guitar players who would plug right into a PA and go for it. All I have met want their favourite amplifier on stage with them.
Output impedance at 0.5Ω won't happen. It takes too much design investment to do so. To get the same power levels into the other impedances would require a bulky transformer to match the amp into the various loads. Look how many in today's market work into 4Ω at the lowest.
It;'s all well and good each of us making a feature list of what we want from out amplifiers. Manufacturers need to sell a decent number of identical units to make a profit. Your wish list would be very different than mine. No-one can produce 'Swiss Army knife' amp that will suit every player out there.
Keep safe and healthy.
Well good luck to you too but you are missing out on some of your amplifiers' capabilities. Remember that you are not getting the full output from your amplifier all the time. Amplifier designers are cognizant about how impedance varies with frequency. It's one of the design considerations.
One thing to bear in mind with Trace stuff is that their amps seem to be rated at peak power. The GP7 300 that I have is in actuality a 150W amplifier. Surprised me all to hell! On top of that the cooling path for this particular amp is very poor. It's a fan blowing on the heat sinks. There is no 'in' or 'out' path for the air.
Why not diagnose what the problem actually is before pulling the tweeter and finding the chuff still there.
Remember pulling it too often makes you go blind! LOL
In my mind you use whatever you have to get the sound you're looking for. My own system resides in a four space SKB rack case. The cabinets are a pair of Acme 2x10s stood on their ends for a vertical 4x10. The case is wider than the cabinets and I don't give a damn!
I use 4Ω Acme B2 cabinets. They are a 2x10 three way box. Aside from bass I have used them as PA mains and also as subwoofers in my larger PA. Everything that I throw at them is reproduced cleanly and without effort. Playing a Low B through them is a pants flapping revelation. I use a pair of these with my bass in a vertical 4x10 stack driven by a 2KW Class D power amp. I own four and when I use all of them it's delightful!!
Properly designed amplifiers take this into account. I have never experienced a problem running two 4Ω loads per channel on any of my power amplifiers - neither did I expect any!
Back in the day JBL wired their woofers such that a positive battery terminal to the positive terminal on the driver would cause the cone to pull back into the magnet. Usually the reverse is true.
But what would you know? You were too busy saving the planet from the Mekon!
Keep safe and healthy!
I've read about the lack of support on my side of the Pond. It's sad to hear it's universal. The only way past it is for folks to quit buying their products. Good support policies are what leads to fresh sales. I certainly wouldn't buy a Mark Bass product.