If they are midi files, then any cubase version will be fine - on the other had are you talking about the old .all files or the newer .cpr files? I used an old copy of SX3 to convert my old files to .cpr. Cubase 8 seems to open all my .cpr files, but won't open .all and Cubase 5 couldn't open them either. I no longer have SX3 that I can find, so I cannot open any old projects. However, as I no longer have many of the hardware synths from then either, I guess it doesn't matter to much.