Hm. Let me try to elaborate on that a little, perhaps it gets across better.
Both XR and OS consist of two things: the core systems and vessel-SDKs. The core systems do generic vessel sounds and goodies like MFDs and such. With the SDKs, other addon developers can do vessel-specific sounds. These vessel-specific sounds are additional to the generic vessel sounds the core systems deliver.
The problem now is that once an addon is compiled, you can't change the SDK it uses anymore. So once you have one core system running, vessels with the SDK of the other system don't emit vessel-specific sounds anymore. Generic vessel sounds are still active, of course, because they are done by the core system itself.
For the vessel-specific sound problem, there is the sound-bridge solution: it acts as if the other core system is also active, but just passes the vessel-specific sound action through to the installed core system. That's really all it does, nothing more.
If I understood you right, your main concern is having the OS5 MFD and the corresponding jukebox-function. For this, I'd suggest to install OS5 as core system, as well as the corresponding bridge from XR SDK to OS5. With this, you will have:
- all OS5 features including MFDs
- full support for OS5 vessel-specific sounds (i.e. addons compiled for OS5 will fully function)
- bridge support for XR vessel-specific sounds (i.e. addons compiled for XR will have functioning vessel-specific sounds)
You will not have:
- XR generic sounds (i.e. various ambient noises and generic call-outs, e.g. "welcome on board, commander")
- XR features (e.g. configuration file settings to map sounds individually)
If your main concern is the lovely voice actor's call-outs from XR, though, you can instead install XR as core system and the bridge from OS SDK to XR. With this, you will have:
- all XR features including generic cockpit sounds
- full support for XR vessel-specific sounds
- bridge support for OSx vessel-specific sounds
You will not have:
- OS features (e.g. MFD and jukebox)
- OS generic sounds
You can't have all of the above advantages with any combination, though. You'll have to decide.
Perhaps it is possible to install both core systems and configure them to mix and match sounds via filters, but I don't know if this is even possible for all setups right now. It certainly is non-trivial and hard to maintain. I guess you would be on your own with such a Frankenstein solution.