I used to own the Twin Mk 3's, and have heard the JM Labs at a dealer. Both are VERY nice. But personally, I think if you are going to upgrade the 3's, wait a bit and go for something even better than the 906's. While they are great, I don't know if I'd say they do everything better than the Twins, which seemed to have a certain magic to them, depsite not having all the supposed "hi-fi" trickery.
I paired the Twins with a noname British integrated called the Newtonia Solis in a second system. The Newtonia was an incredible performer, having much of the pace and musicality fo the Naim gear, with bass and dynamics to boot. I miss that combo; I sold it when I dismantled the second system....
So I'd say stay happy with your Twins, and upgrade when it is even more worthy.
My thoughts.....
(FYI, I heard the JM Labs driven by Naim and Musical Fidelity gear).
I paired the Twins with a noname British integrated called the Newtonia Solis in a second system. The Newtonia was an incredible performer, having much of the pace and musicality fo the Naim gear, with bass and dynamics to boot. I miss that combo; I sold it when I dismantled the second system....
So I'd say stay happy with your Twins, and upgrade when it is even more worthy.
My thoughts.....
(FYI, I heard the JM Labs driven by Naim and Musical Fidelity gear).