DTS X - Backwards Compatibility Issues

[bga84]

Hi

Sorry if this has been covered before - I've not been able to find any mention.

I have an Onkyo HT-S5805 Dolby Atmos system and an Oppo 203 UHD player. I had believed that although the HT-S5805 is not DTS X compatible (and could not be updated), I would still be able to play DTS X discs because the HD-MA core was still there.

A little over a year in to having this set up though and I can still only get sound via DTS X discs (all Universal UHDs it seems) if I go into the Oppo setup menu and select LPCM audio format. It's a pain in the behind because I then have to switch back to bitstream if I want to play an Atmos disc.

Am I missing a trick? Is there a way of getting the HT-S5805 to recognise the HD-MA core on a DTS X track?

Thanks!