The MX-6S is a passive resistance mixer originally bearing three RCA connectors feeding the AUX channels & three 1/8th inch monophonic miniature jacks feeding the MIC channels. The center MIC/AUX channel is switchable to the destination of output channel 1 or 2, which took the form of ~2 foot pigtails terminating in 1/8th inch plugs.
I can begrudgingly support both RCA & 1/8th inch miniature in the studio; pigtails, however, have to go & since I've going to be in there already...
Removal of existing output wires is as simple as desoldering the points on this circuit board (upper grey wire shown here is channel 2 output, whereas channel 1 was connected to the fifth & third notch at the lower right of PCB) and pulling the wire out. Pulling the wire was further simplified through studied application of snips.
Rather than destroy the 3x RCA jacks to harvest the phenolic mounting board, I fabricated a new one out of mild steel to mount the 1/4 inch phone jacks, the original MIC connectors simply unscrewed to allow drilling the phenolic out to accept the larger jack. Further drilling was required at outputs. The MIC inputs are a rat's whisker away from an interference fit with the switch bracket, this probably wouldn't have been a problem if I hadn't run out of open frame jacks.
Output is further modified with a switching jack that will route channel 2 output to channel 1 if a cable is not plugged into channel 2.
Much better. The two input banks are different from one another: AUX is set up for line level with a 100K log as volume, MIC was originally terminated across a 560 ohm resistor feeding a 5K log as volume. This is equivalent to different gain structures when fed by something that is not loaded down on the MIC input (I opted to not reinstall the 560 ohm load resistor) in my very limited experimentation I find the higher impedance inputs far easier to control.
Worked like a champ, I expect it will see a lot more use now.