Hotter than a 12AX7? Nah, the AX7/ECC83 is as hot as they come. You could try swapping out a few different ones to see if it helps.....if you can even find the damn thing in there among the SS components & ribbon wires.
Don't expect your AVT to sound like an all tube head
regardless of the Marshall ads. All tube and hybrid/SS amps are totally different beasts.