First a couple questions.....
Does it have the be THE MTD sound (not sure I really know what that is) or something more similar to a particular artist's sound, who happens to use an MTD?
Or does it just need to be something other than the Stingray sound you are getting?
Can you isolate the differences you want to see to tone elements (more/less bass, more/less mids, more/less treble, better sustain, more/less growl, more/less punch)
If you HAVE TO HAVE THE MTD sound, chances are you need to consider getting an MTD. Maybe that involves selling or trading your Musicman. If so, you DO NOT want to mod the Musicman. You should be able to get a used Kingston Z or Kingston Heir type bass for about what you can sell a used Musicman for. Maybe even a little less. If you mod the Musicman, the selling value will drop like a stone.
If you just need to enhance or de-emphasize certain aspects of the Musicman tone, consider outboard preamp / Direct Box solutions first. Then maybe look at some other sort of signal processing like a multi-effects unit. Take your bass to a music store and experiment with the DI boxes the have. Try to play through amplification as close as possible to what you normally use. That will be your lowest cost approach. Playing around with the settings you can get on a Radial BassBone, a SansAmp BDDI, or a Line 6 Bass Pod could help you get close.
I also am not certain that there is ONE MTD sound. In my opinion, the MTD USA series is the most wood sensitive of the major boutique basses. In other words, an ash bodied, maple necked MTD will sound significantly different than an alder bodied wenge necked MTD. Not so much that I can identify one or the other blindly, but if they are played A/B, I can hear the differences. If the sound you're talking about is more the Kingston Z sound or the Kingston Heir sound or something like that, you'll be better off just selling the Stingray and buying one of those with the proceeds.
I am not anti-modding (I've modded several Fender Jazz basses and one of these days will get around to assembling a P-Bass I have in pieces). The thing is, Stingrays have such a distinct character that most mods you could make will de-value the instrument.
Good luck finding that sound!
Peace,
James