That's what I have heard. The SF6 can take a 16M Bung expansion board, but I don't believe they work with the 32M or 64M Tototek expansion boards. Tommy was very specific about the subject when I asked about it. SF7 is required for using their 32m and 64m boards.
Correct me if I am wrong, but I thought compatability had something to do with the memory modules Tototek produced (Timing/Latancy?). If you used original BUNG memory it was ok. I think it was mentioned that for stability purposes, only use the modules listed for the according system.