The pin-out for MM-100 or LCD-S20 cable connector at the headphone side is the following:
TRRS:
Tip - L+
1st Ring - R+
2nd Ring - L-
Sleeve - R-
The wires in the headband are connecting via two TRRS connectors in parallel, so it's not important which side the cable is connected, left or right. Both versions can be used, single ended (TRS) or balanced (TRRS); the left speaker will always take only the left signal and the right speaker will always take the right signal.
Making this cable balanced will require splitting the L and R channels into appropriate pin-outs for your amplifier.
Here's a diagram for the internal wiring to give a better picture of what's happening (this is also true for LCD-S20):
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Custom cables (for standard, single-ended or balanced amplifiers):
As shown above, neither MM-100 or LCD-S20 use a standard 3.5mm input like most other headphones. This means that many widely available 3.5mm cables will not work as intended (i.e. standard, dual sided y cables that connect to both cups). The cables need to be pinned specifically for the MM-100/LCD-S20.
While we don't officially endorse any specific brand for this, you may find some custom cable makers online that may be able to provide single ended or balanced cables that work for the MM-100/LCD-S20.