When did Michael tell you this? I know he changed his preamp starting in Jan 2020, and this bass I was trying had the new preamp as it was a build from earlier this year. I can tell you that unless the trim comes from the shop at maximum setting that's not where this 534 was set (I presume it's halfway up or so, but I could be wrong), and as I mentioned we swept up and down each EQ knob and there was nothing I would perceive as abnormal behavior, or the amp not having appropriately matched gains.
The other reason I'm skeptical of this being an issue is that the MTD in question has the same relative output as the other two basses (passive Jazz with GZRs and Spector with BTS preamp trim set at 50%), and all drive the amp exactly as expected. The bass did not require 'everything set at 10', and FWIW the front end of the Aguilar did not sound that different from plugging straight into the effects return, which we also tried.
I guess I'm surprised because I was expecting not to like the Aguilar at all with the MTD, and was expecting something along the lines of too much color, which turned out not to be the case at all. Next time I chat with Mike about my build I'll ask him his thoughts on it -- maybe it was an issue in the past and is no longer a problem -- but I won't comment any further on this since I own neither an MTD (yet) nor an Aguilar ToneHammer (nor any other Aguilar equipment!).