I agree with @oberoniaomnia - trust REL and use the stock cable.
If this is a line level signal then 24 awg is quite typical and sufficient. If you don’t use the REL cable, I would recommended soldering SpeakON connectors to any reputable bulk shielded audio interconnect (Furutech, et al.) or bulk professional mic cable from the likes of Mogami, Gotham, or Belden. However, I seriously doubt you would ever discern a difference between those options and a cable from REL. Rabbit holes are usually a waste of time and money - I know because I have been down many of them.