Since you are a DIY and a pedal guy, you can address both of those issues with one of there...
https://aionelectronics.com/project/lum ... nic-stomp/The tone-shaping capabilities of that pedal are simply amazing. Put it last in your signal path and any issues in the top or bottom end can be fixed right up... mostly.
However, there is only so much you can do to fix the "boxiness" of a small 10" cabinet. It's just the physics of sound limiting you there. It is pretty dramatic when you hear the same speaker in a small 10" combo compared to a large 10" detuned cabinet. Doesn't sound like the same amp!