Connect External FX using SPDIF

Hi, I’m trying to configure an external FX (Lexicon PCM90) connected using SPDIF and can’t work it out. I’m using Cubase 11 and Focusrite Control with a Scarlett 18i20.

In Focusrite Control settings I’ve set the Digital I/O Mode to S/PDIF RCA

In Cubase ‘Audio Connections - External FX’, when I create an external FX I only seem to have the analogue outputs listed for the send bus and for the return bus I can see Input 1-8, loop 1-2 and digital 1-10. Is there a mapping I’m missing somewhere?

Any guidance would be appreciated. Thank you, Oliver

Maybe you should check the manual of the unit. There could be a description of the digital I/O.