I use Mconnect too! So i can answer your question (Great app btw).
Mconnect cannot do the first unfold of MQA, now this is not a problem as the Gustard X16 is capable of doing the first unfold. However, the first unfold only happens via the USB input, not the SPDIF input.
To solve this:
1) use the Tidal app to directly stream to the Chromcast, thus doing the first unfold in the Tidal App
2) replace the Chromcast with something like the raspberry pi that has a USB output.
Thanks for the replies, unfortunately I can't get my head around your advice
If I use the tidal app (on Android) I can only cast in Hifi which is 16/44.1 (?) Feeding this into the SPDIF on the X16 won't give sufficient data for MQA decoding?