I would test each component to see if they are all up to snuff. Test the speaker first through the other amp. If thats OK Then use the other amps effects loop to see if the SMS preamp (plug into effects receive) works well. If the SMS is OK, then plug the blues deluxe into the mesa through the effects send.You'l have to see if all are working properly.
That rig is a hell of a stage rig, maybe opening it up some (louder than most would enjoy practicing) would yield what you're looking for. Also if you don't have a buffer maybe try cranking the guitars volume to 9-10. Make sure the tone knobs are cranked too, then adjust to taste. You can also try doing a short run from guitar to a boss pedal in bypass to use its buffer. That is what I would try in your shoes. If you have the money I would seek out a tech and have him go over it tho.. Good Luck!!