MO 4Media (and I think JRemote too) has a "Theater View Remote" interface that can be used for this. It sends key presses to MC so you could do the selection in the OSD like Hendrik describes.
After some searching, I found that if you stepped back to the first screen on JRemote after selecting a movie then there was a button called Remote that enables you to swipe up and down on the screen to activate the OSD. It's far from being an intuitive interface but at least it works. Many thanks for bringing that to my attention
However, I have failed to find the equivalent feature within MO 4Media.
EDIT: My previous comments implied that the developers of the remote apps for JRiver might have been lacking in sympathy for deaf users. I must now apologise for that unwarranted suggestion, but perhaps they could have done more to publicise their efforts in this area. None of the previous threads I found where users were asking for advice on this subject ever mentioned an OSD-based solution and 168 people read my post before
cncb came up with the answer, so it is clearly not widely known among the JRiver community. I'd never even heard of the OSD before and I always assumed that if any subtitle and/or audio selection facility existed then it would be located on the remote app's Playing Now screen (as it was on the Oppo interface I used to use for playing my MKV files).
In an attempt to make this thread a comprehensive guide to the topic, I have been looking again at all the remote apps. Gizmo passes the test, as I have now found that if you tap the 3 dots icon at the top right of Gizmo's Home screen this offers you the ability to select Mode. If you then select 'Use device as Theater View remote' you get a screen where up and down swipes allow navigation of JRiver's OSD.
As far as I can see, no such facility exists within Panel and I've still not found how to do it in MO 4Media.