As to balanced cables being immune to quality differences... that is just silly talk.
@mambacfa, no one is claiming that balanced cables, in general, are immune to quality differences. The Makua preamp, specifically, is said by its manufacturer to be "amazingly immune to influences like mains quality and choice of interlinks." The OP’s question was:
Are there other gear people have owned where the designers eschewed higher end cables? I am curious as to what aspect of the design leads to this type of statement.
The link I provided in the first response to the OP, which is to a post by a highly experienced designer of renowned high end equipment, explains that equipment can be designed to be largely or entirely immune to differences between balanced interconnect cables, although in most cases it is not. And he states the technical criteria which are necessary for that immunity to be realized, as well as providing what I consider to be compelling proof of his contention.
Regards,
-- Al