This is a user to user forum, as QuickTimeKirk suggests you need to use the Apple feedback pages.
I do however share your pain, it does seem the Mac hardware is capable of this based on reports from users running Windows via Boot Camp. Since Apple have not themselves supported Blu-Ray discs which are the predominant source of media using these formats Apple have not up-til now made any effort in this area.
It is actually my own experience that all the streaming services - even those offering 4K video actually only provide inferior quality audio streams. This is something the streaming services are starting to look at but have not yet resolved. This includes Apple's own iTunes Store movies.
As you I believe mention, Apple have finally announced support for H.265 video which is the format of choice for 4K videos. Apple have not indicated yet what additional audio formats if any will be added with this, they could stick to the same ancient Dolby Digital 5.1 equivalent to DVD format which is at best what streaming services currently offer.
You need to remember Apple target almost exclusively consumers and those consumers using Apple products. So H.265 is being targeted at users of the latest iPhone and iPads for recording 4K video and obviously iPhones and iPads are not going to record surround sound audiophile i.e. Blu-Ray level quality. What we can hope for is that as finally FinalCut Pro X is also going to support H.265 for production this might also mean Apple support these Blu-Ray level audio standards in FinalCut Pro X for the same reason and this might as a side effect mean playback is also supported.
It could however be that Apple decide to pinch pennies and not license these audio standards, clearly Apple do need to worry about such costs. 😉 What is really annoying is that Apple's current approach even prevents other developers licensing these codecs and 'passing them through' aka bitstreaming them.
Realistically this is only going to change if/when Apple finally start offering 4K content via the iTunes Store and upgrade their audio support. Remember even the current 1080p aka Full HD content on the iTunes Store only has 5.1 Dolby Digital audio.
Note: High Definition Audio can be confused between two different things. There is what is actually the intent in this thread which is the lossless audio formats used by Blu-Ray and UHD movie discs, and what is more commonly associated with the term High Definition Audio which is music in a format superior to ordinary audio CD discs. Apple do not support either. Considering Apple have always and still claim to have music in their blood, the fact they still only offer 256Kbps AAC music is an abomination. 😢
