MXR 6 or a compression pedal?

Howdy folks! I'm a rhythm guitar player for a Thrash/Groove metal band, I'm currently working with a 4 pedal setup dialed in for a low end, high gain crunch.

Amp - Marshall JCM900

Cabinet - Marshall 4x12 1960

FX loop - noise gate, puppet master eq, chorus.

Front amp - ibanez TS9.

However, the crunch it's not as "air tight" as I want it to be, after doing a bit of asking around, I was pointed to either the MXR 6 band eq for the front of the amp, or a compression pedal, does anyone have an ideia on what I should go for?