I'm not a huge transistor Sunn (or for that matter any transistor MI amp) fan, so I don't know a whole bunch about them. But, I think the Concert Lead and Concert Bass, and the Beta Lead and Beta Bass are voiced pretty similar tonally so I don't know if that's the answer.
What about a low pass filter, or probably even better just put a nice graphic EQ in front of the amp? You could attenuate the frequencies you don't want at will.
I have a nice Sunn dual 30 band w/ power supply that I just pulled out of a monitor rack that I upgraded, I'll list it here before it goes to eBay.