OK I managed to install Spotify on it, using the direct .apk link that Joe mentioned above
So the issue here is perhaps not the 'security' side of Android (install from unknown resources etc), but could be that apps must be within the 'whitelisted' list within the fw
Will try and get Tidal's .apk file.
I'm hoping that the final version (at least for the batch for the western market) will have Play Store pre-installed, I know Xiaomi is starting to do that for it's phone and tablet, they are preinstalling PLay Store for the export batch.
[EDIT] Another thing - last night I was listening and A/B-ing with X5 (with Dunu DN-2000J and Fidue A73), when I finished, I noticed the battery was at 85% (from full charge, and about 1hr listening, which is fair enough) - I went to work this morning, took the unit, and I was getting ready to do some more listening, but the battery was at 35%? Looked little strange to me, will do some more battery testing in the coming days