I have left Audirvana Plus version 3.2.18 installed from the time I upgraded to the “new” Audirvana 3.5.xxx.
This was a hedge against issues with the new software so that I could always revert to a known, properly-functioning version. In fact, this has come in handy when new issues came up with the latest version.
It has always been possible to play EITHER version without a problem but, of course, NEVER running them concurrently.
I did not mention that this problem occurred suddenly without any Audirvana version changes [3.2.18(3702) & 3.5.33 had been in place for some time].
The only difference I can think of is that as part of a general system maintenance, I reset both PRAM and NVRAM on my MacBook Pro (mid 2015) running macOS High Sierra version 10.13.6.
Also recall that, as an experiment, I deleted the existing 3.5.33 version and downloaded a free copy which did NOT solve the problem. (This should have updated all associated files…)
To summarize I have previously had no issues with any files (MQA or otherwise) playing on either version of Audirvana and even use the TIDAL macOS app (currently 220.127.116.118) with no problem - as long as they were not running concurrently.