Hi. I’m not familiar with dietpi or roon - so it’s possible you will already have all you need.
My preference (and what I do with a similar set up) is to use Picoreplayer (as an alternative to DietPi) to drive the katana/pi. It will be able to see the LMS on your vortexbox.
Using picore will give you some digital EQ (useful) and filter controls (I can’t tell much difference) over the katana
You can control the whole set up using iPeng (apple) or orange squeeze/ squeezecommander (if it’s still going) on Android.
Make sense?
Simon
MINI DSP SHD; Longdog 300b; Reiver Fenwicks
Twitter @siashmore