I would assume the M60 sound similar to M22ti, they're very accurate and great sounding speakers, adding the pads probably would ruin the overall SQ, imaging, and sound staging to a degree, maybe my ears are not as sensitive as yours but if I were you, I would of bought a more laid back speakers, such as something from KEF, and many other warm sounding bookshelves or towers out there.
Another suggestion, instead of adding pads, ever thought about putting a thin layer of mesh or whatever on the speaker grills to dull out the sound? perhaps you could get a decent EQ to smooth things out too!
