So what was the end result here? I am wanting to upgrade my MM as well.
Well, there are a lot of options.
Marcus actually uses a Bart TCT preamp (the original install by Roger Sadowsky). If you need exactly that sound, that's where you need to go. Big issue is that for whatever reason

Bart only offers the module. You would need to get a schematic and get the rest of the components from Bart and elsewhere. That is a great sounding preamp; but, Bartolini has gone mostly in the direction of 3 band circuits.
Meanwhile, the Sadowsky preamp is readily available these days. I just had Pat Wilkins install one in my "player" bass. It's an easy install, if you have soldering capability. I sent this one to Pat, because my bass also required some routing that I wanted done correctly. Pat is a cat.
The Audere is another great option. They have a 4 band, which to my ears sounds more useful than the 3 band circuits. You can hear examples if you search YouTube for the Wilkins Road Tested basses.
And I believe Nordstrand may now have a 2 band circuit which is probably nice; and I've heard whispers of a Pope J refit circuit in the works. Lots of options. Life is tough as an electric bassist. Do you want the prime rib or the filet?