"Every speed control I have ever seen, is an external box that you plug the motor into"
The Phoenix is different because it uses a small magnet that you put underneath the platter and then a small pcb card between the platter and the plinth so it can read the magnet, kind of like a strobescope.
The VPI might work, as long as it sends out AC, correct?
I am surprised that no one has come up with something like this for idlers. I mean, they make every audio gimmick in the book now, and this no gimmick but a real need; weird.