Improvements to Technics KN5000
This is ready for review and replaces PR #11835 but does not include the kn1500 driver, which I'll leave for a future PR.
After @ajrhacker made this comment (https://github.com/mamedev/mame/pull/11835#issuecomment-2307930039) I investigated the problem a bit more and I was able to get rid of the segfault on the extension interface for the Technics KN5000 (which is used to install the HDAE5000 board).
I've just force-pushed the amended fix.
I cribbed a small part of this in 23e9abc97c8923f1d7e948a68dc2896084972d29 as a release is coming very soon.
This one is finally done (via a larger number of smaller PRs merged separately).