Just thought I would do an update on my current set up, a GK MB210 with MBE115 cab, I am delighted with it, I have lined both cabs, have done the back walls with foam egg crate sponge 40mm thick and the other walls with polyester batting 25mm thick, all stuck on with that instant grab spray adhesive, I have not braced the cabs, the MBE115 has some very good bracing built in anyway, I have been out with my band this evening and the amp was on the following settings;
gain - 12 o clock
master - 12 o clock
boost - 10 o clock
treble - 10 0 clock
high mid - 10 o clock
low mid - 1 o clock
bass - 7 o clock
I used my MIM Fender Precision, I have found the lining does make a small improvement to the sound but the real cure to this amps boominess seems to me to be in the EQ and boost, as you can see I was only running at about half capacity but with the bass almost on zero and boost down, I play mainly with my fingers but with a pick there is very little boominess, shame as I play 95% with fingers, but at least I now have it under control .
It seems crazy but there is too much bass in these amps in my opinion, even if it had half the amount of bass it would still be a huge amount, any more than half is way too much bass !
It is a great amp though, to walk from car to studio with an amp in one hand, the cab in the other and my guitar on my back is brilliant

To anyone who wants an MBE210 to go with their MB210 but cannot get one still, I would recommend an MBE115, it makes the MB sound huge .