They have a built in HPF. The only other thing I wonder is if you had the vintage button engaged. That thing is mud city.Yes! Tried some pretty extreme eq settings. My GK MB112II was a night and day improvement in terms of muddiness in the space, but the preamp doesn't behave so well with my tech 21 vt. I'm hoping for a middle ground between the rumble and GK. I think the Rumbles would really benefit from a HPF, just haven't tried it.
Surprisingly the 200/15 is also a lot better and clearer sounding amp than the 500/210 for whatever reason