Too lazy to uninstall Sierra and revert to El Capitan, I've achieved a more or less stable system by:
- not booting any programs at logon; specifically, WD's drive utility, which is required to install their 2-bay mybooks amonghst others, has not yet been updated to comply with Sierra. This caused lockups at boot, on my MBP.
- switch NAS to SMB file transfer protocol. Solves the perpetually spinning ball when trying to directly access files from Finder; however prevents Time Machine use on the NAS. A colleague of mine has actually chosen to continue to run time machine succesfully, as long as he doesn't access files directly, so it seems either-or at the moment, until Apple solves this (if ever). YMMV
- Finder still occasionally refuses to access the NAS under SMB, in which case I force restart Finder from the apple menu. Really hope this gets sorted in 12.1
- When directly working with folders on the NAS, there is an ocassional apparent clash between Apple and Synology access rights, preventing for instance the moving of folders. Disconnecting and reconnecting the NAS solves this, temporarily. Again, hope a future update of Sierra and/or DiskStation solves this.
- For those running Audirvana+, you have probably already noticed there is no direct mode under Sierra. Apparently you can hack direct support back in - but it's the type of hack that you'd have to do every time there is an update to the OS. Without direct mode, the Mac sounds somewhat compromised compared to what I'm used to, but as I'm not running a mac music server at the moment, not too bothered myself. For now.