my new 604 cabinets I'm building.

[voice of the theater]

I won't be surprised if your new cabs (if properly tuned/ported) end up sounding way better for your 604's than the AS-101 cabs that your 604's are in now. I still think someone may have pulled 416's and 811's out of your Heath 101 cabs and stuck the 604's in there without any regard to the cabinet's size/tuning/port size being appropriate for the 604's....... Maybe that's why they sound "boxy".......