[LAD] MIDI SysEx "7 (Signed)"

Hi, I'm writing a CLI editor for the Matrix-1000. Regarding to the owner's manual some parameters have 6 bit values, so I gave them a range from 0 to 63, for the 7 bit value I definite a range from 0 to 127. Many values are described as "7 (Signed)". I consider those values should get a range from -64 to 0 to +63, IOW I understand it as a two's complement, but the editor of my Atari ST's Cubase 3.1 doesn't give them a value from -64 to 0 to +63, instead the GUI's value range is from 0 to 127. I suspect that the Cubase editor is mistaken, resp. the editor was build by a "kit" and I suspect there's a limitation, it doesn't know signed values. My guess is, that it would be correct to assign a value range from -64 to 0 to +63. Is this correct? Or am I mistaken and the value range given by Cubase is correct? Regards, Ralf