I have a rather unique Sigma, meaning that I didn't see any mention of it here after reading this whole thread (unless I missed it, lol). It is a DV-4M. A while back I did do some exhaustive research on it and found little info, but I did find some. At any rate, I acquired it a yr or so ago in pretty much "new" condition. It looked like it had never been played or even handled much. I fitted a bone nut, saddle and bridge pins from Bob Colosi on it and it really sounds good, exceptionally good! If any one can provide additional info about this model I would appreciate it,,,thanks.
PS - I tried a few different strings but this guitar really came alive with Dean Markley Alchemy goldphos CL 12-54s.