After some troubleshooting, it seems to me that Synology VMM only works when you have an intel processor matched with an intel DSM bootloader.
So, that would mean one of these:
- DS3615xs
- DS3617xs
- DS3622xs+
- DS918+
- DS920+
- DVA1622
- DVA3221
Unfortunately, none of these supports 'native' NVMe storage. This apparently gets increased under DSM 7.2, but that is still in beta. Moreover, some don't even officially have NVMe ports (also not for cache) not supporting this kind of storage at all.
Anyway, seems to me like the DS1621xs+ would be the best of both worlds, but unfortunately that one is not available...