Process audio via hardware, then back in

Hi guys -
I want to be able to process previously recorded audio via an external piece of hardware. So I need Cubase to be able to PLAY the audio, while simultaneously RECORDING the new audio. This seems rather basic, but I can’t get it to work. I get an error.

Any suggestions would be most appreciated.

I’m running Cubase 9 via a Focusrite 18i20.

Set it up as an External FX in Audio Connections.

FYI the Issues sub-forum is really here to post about problems with Cubase itself rather than ‘how do I get this to…’ questions. No problem posting them here but a lot less folks look at the Issues forum than the General forum so you have a much better chance of getting an answer there.

Cheers Raino.
Really appreciate the advice on all fronts!