I hope I understood correctly.
You want to hear only the channel 9 on the headphones/main out1-2, and play out the channel 1-8 on the DB-25 connector?
You can do that easily.
Mute the 1-8 channels or solo the channel 9 in the monitor mixer (channel focus mode on the uTrack24, or uRemote mixer; or exporting the song from uTool you can set up the mixer as well) in this case you will play out the solo channel(s) on the headphones/main out 1-2.
The auto fail safe thing can be solved really soon with the coming sync feature for redundancy.