Follow up to earlier post.
Bluetooth connection perfect. You can pair any device from the app (you don't have to be 'on' the device you're connecting), or just connect to 210 in the Bluetooth settings of the device you want to connect from.
If MHR is selected, it is sent to all outputs so the co-ax out is useless. With MHR de-selected, both outputs work fine.
The app appears not to (always) remember the connection "no devices found" and you have to reconnect, but as I said before, I'm not sure when you need the app unless you're changing configuration. Switching between Roon and bluetooth and vv is fully automatic. I imagine anything connected to the SpeakerLink input might do the same.
Re MQA, this is what the app says:
The Meridian 210 includes MQA core technology, which unfolds an MQA file once to recover all the direct music-related information.
The audio is output from the 210 at a sampling rate of 88.2kHz or 96kHz. The final unfold of the MQA file is carried out if the output of the 210 is fed to another Meridian product which includes MQA renderer technology.
Is that different from what's been suggested elsewhere in this post? I don't have full understanding of MQA yet!
I don't have any MQA sources, opinion here seems to be that MQA through Roon isn't a proper implementation (is that right?). I might try a Tidal trial just to see what happens; I know there are some free MQA downloads - I assume I just dump these on a USB stick and go from there.