Roon is usually just using the first 8 channels. So do you hear sound when you connect something compatible to the analog 1-2 channel outputs?
Note: Roon is not a mixer software. You may need something like a software that provides a virtual sound card (compatible/seen by Roon) and properly setup with/for your Motu multi-channel audio interface to be able to use it as you wish to. You can also find older threads about that on the forum: Search results for 'multi channel interface' - Roon Labs Community