Agree - something is wrong. I run the SMS at about 10 o'clock with the MC50 at about a third... single D130 and it's friggin loud. Cranked up it's louder than my 50 watt plexi with a 4x12.
Don't under estimate the importance of good preamp tubes. A 12AX7 has potential gain factor of 100, but that doesn't mean yours do. I have a few (my best ones) that are in the upper 90's, but a lot of them re lower and as a result are less loud. If you run new manufacture pre's, and the gain factors are often around 60-80 and early in the circuit that can have a pretty big effect on overall volume, but I suspect something else is in play as well (by the way this often explains the apparent difference in volume people notice between the two channels of blackface and silverface amps).