You should really be looking at the REL ST series if you want tight musical bass, the Q series sound a bit sloppy in comparison. The REL Stampede and Strata 5 would both be good options.
As for the MJ subwoofers, I used to be a fan, had a Reference 1 for a while. That was until a colleague of mine was playing about with one and happend to have it hooked up to a stereo system without any other speakers attached. It was then I noticed I coulod hear midrange and some treble coming through the MJ subwoofer. We tried lowering the crossover to its lowest point, still there was noticeable leakage coming through the crossover of frequencies that shouldn't have been there. We tried this with several other MJ models inluding my own and they all did the same. I have since purchased a REL Stentor 3 and have not looked back.
If you are on a really tight budget then the Quake can be quite musical but I wouldn't bother with the Q150 or Q201 for music. Ultimately though you should really go and audition all of these subs, we have everything up to the REL Storm 5 in our store and I think many other stores will too.