The external added some much needed top end chunk. The whole things low mid voiced so the external boosts really compliment it better and balance it out. The internal boost seemed to just give more of the same type of tone the amp already has imo which isn’t a bad thing, but sort of limited.
These airis ss amps sound great. I had a 51 filthy a little while back and I liked it a lot (although I liked my 5150 better lol). I’m happy there’s someone still producing higher end solid state amps.