While I am not an authority on this, you really should call Vandersteen to verify, the entire model 2 series is NOT upgradable. I had 2Ci's for about ten years and never came across any upgrade information. The Vandersteen website says nothing about it either. I aksed Richard Vandersteen about this a few years ago and I beleive his reasoning was economics, a $1300 speaker can't have that built into it, whereas the $2500 model 3 could (of course the 3A Sig is now $3500!).