The M-Pulse line (Walkabout, 600, BB750, V-12) are going to be more similar in overall tonality to the DB750 than is the M6 Carbine. My guess is that some of it lies in the tube versus solid state MOSFET driver, but either way you look at it, the M6 was intentionally voiced for a more articulate, fast, clear tone than the more full, warm M-Pulse line. This is not to say that the M6 is too dry or clinical. It's not, and I give Mesa/Boogie great credit for being able to achieve that degree of articulation and clarity, while retaining a musical sense of smoothness, and some warmth. But the other 'hybrid' Mesa/Boogie amps are more burly in the mids, and more warm in general, making them more akin to the DB750, which can be very beefy, warm, and burly.
The M6 is much more tonally flexible than you might think, though, and there are lots of tones to dial in. And in truth, the DB750 is also more flexible than you might initially expect. So, depending on how you dialed in your DB750, you may or may not be able to hit something close with the M6. They have different starting points, but there is some overlap.
Tom.