Several references
Thanks for doing the work to back up your comments. My apologies for taking so long to reply.
First, note that most or all the sources you quote are old, either from before the X32 was introduced or slightly after. There has been a lot discovered since then, and the price and availability of CAT6a (for example) have respectively plummeted and soared. So using higher grade CAT cable is not the burden it was at that time.
Second, I have not been able to find any documentation that using a higher resolution cable diminishes performance of lower resolution signals, although you say:
Some cat6 cables with a lower twist rate (2 twists per cm) should work fine, but others with a higher twist rate will not. This is not a problem in ethernet networks because of the way ethernet works, but AES50 only uses the physical layer (OSI-layer 1) which is the connections, but everything else is different, so it can not be held to the same standards that ethernet based networking (hence why you can't use ethernet switches and other network gear on an AES50 network) is which is where most people make their mistakes.
but I couldn't find a source for the higher-twist cable not working for AES50 in any of the documentation you provided. Or anywhere else.
The fact that Ethernet switches do not work for AES50 is a red herring, since AES50 and Ethernet are different protocols. You CAN extend AES50 using AES50 extenders but there does not seem to be a hub/switch equivalent.
Lastly, AES50 is a Standard agreed upon by manufacturers, scientists, and other interested parties, and the resulting equipment is built to conform to the specs in the Standard document.
The entirety of the Standards document (AES50-2011) that relates to the cable is:
"4 Physical Interface 4.1 Physical medium
"HRMAI uses a four-pair twisted pair data cable. The minimum specification shall be Category 5 as defined by TIA/EIA-568-B.2, although the use of more stringently-specified cable such as Category 6 is recommended.
"The use of screened (shielded) twisted pair (STP) cable is recommended."
The end.
So when that document was written only CAT5 was commonly available (not CAT5e), so although equipment built to the standard would perform adequately, the authors and signatories agreed that "more stringently-specified cable...is recommended". (I skipped over CAT6 because we now know that it has limitations that CAT6a doesn't have.)
Please tell the old wives to stop telling their tales.
*I must point out that I am not an IT professional and have not been trained on this in any way, other than Hard Knocks U plus keeping an open ear for new info to explain these devices that I have and use.
**Thanks to my Internet buddy Robert for getting me to look at the Standards document.