We have recently found the Ernie Ball VP Stereo 25K and the VP Junior 25K to be compatible with our stompboxes. The VP Stereo 25K can control a ModFactor and TimeFactor at the same time using the stereo outs, however you can also use a y-cable with compatible expression pedals to accomplish this.

With the newest TimeFactor software you can also use one expression pedal to control both a ModFactor and TimeFactor via MIDI. 

Alan