I have a near 0 ohm output impedance headamp (SMSL SP400 measured here at ASR)6m would give you 1.32Ω resistance per conductor.
Looks almost identical except that the conductors don't have distinct colors (typical quad colorway), so make sure you beep test them with a multimeter during soldering so you don't mix up the connections.
Thanks for the advice! I'll order this MogamiFrom what I understand, you can't really make use of the star quad magic, since it's intended to transmit one differential audio signal, not two single-ended ones, though it shouldn't hurt either.
(Perhaps double helix would be better, but I haven't tried measuring that yet and also don't really know what I'm talking about tbh)
As for the shield, I'd connect it to the 3.5/6.35mm GND and leave it disconnected on the headphone end. Might actually help with 6m length.