Recently bought some fo.q damping sheets (Ebay) and tried them on just about everything as they are a peel and stick product. Besides putting strips on (a few tubes, transformer, pc and speaker cables, headshell) I also put some pieces on the metal frame that holds the speaker (don't know what that's called) on all four of the M3 speakers. Because I did so many areas, I can not definitively say what did what, but the already capable slam of the M3 Turbos S is even better, with more bass/mid bass articulation, authority and clarity.
Because the open baffle speaker access, this allows tweaking to areas hidden by box speakers so us tweakers have even more crap to mess with!
When I first got the M3's I found a pair of local MIT MH750 speaker cables and even though they are old, compared them with my Morrow Audio MA4 speaker cable. Even though the Morrow sounded fast and clean, the MIT's won out with just sounding right, with more of a natural, organic type of sound that to my ears proved the clear winner. Yesterday I cut open the plastic boxes that house the "interface" and wrapped the area with some fo.q product. Wow, whoda thunk? Anyway, if you're not familiar with fo.q, you can go fo.q yourself (joke) by checking out their website. For $30 or so Ebay bucks, the bang was definitely worth it. YMMV.