Firstly I must say the red channel with boost on doesn't sound that great. For metal tones the palm mutes sound really spluttery and just don't sound right - even when paired with a tube power section it still sounds a bit off. Definitely a usable tone in a live situation but beyond that I'd not have used it.
However after watching Kohle's video on youtube I was able to get an excellent tone on par with my 5150 or any other tube amp. You need to run the crunch (green) channel, with the boost on, and a tubescreamer in front of it to get that modern metal high gain tone. Pair it with a tube power amp with a lot of presence, and a good cabinet and you will have a studio ready tone. Even sounds great with the GPA 100, just with a bit less presence.
Hope this helps some metal players get some great tones