JSX 2x12 can't quite do metal?

[Jax]

I heard the 2x12 combo JSX and was really blown away by the clean tone and a great reverb. The ultra channel sounds like the crunch channel with heavy compression and more overdrive, which is very cool. The plexi-ish crunch channel is killer too, but I didn't get the impression it could really get a more 'modern' metal sound. On lower octave chunky chord riffs the low end kind of falls apart somehow.

I'm thinking the speakers in the combo might be the culprit. If the combo was run through a closed back cab like a bogner, would the low end tighten up and become more distinct? Or is it the amp itself that is sort of sluggish down low? Maybe a tubescreamer would be the ticket?

I really like this amp, but want it to sound slightly more modern and tighter.