There was no difference between the design and performance of the 1.05 and the 1.07, I don’t clearly remember but the change was probably some small layout change on the PC board.
The gain control on the back was put there because lots of users wanted an output control and I didn’t want to change the appearance of the front! In hindsight that was fairly dumb, but I still think appearance is important.
Technically, the SC2 compressor adds to the compressed sound by dynamically adding harmonics during the time it takes to control the volume level. These changes are of extremely short duration and not noticeable, but have a profound effect on the ‘feel’ of the sound. Sounds complicated but in reality, it’s simple, the behaviour of the controlling electronics happens to emulate effects that our brains like; the ‘optical’ compression circuits are much nicer sounding than any other analogue compression circuit, and far superiour of course to any digital system no matter how carefully programmed!