Turns out you can with my A4mk2 anyway! This saves me from so much cables when processing audio 
You just send your audio from an audio channel to the channel that has the A4 plugin on one of the stereo sidechain channels then you select that sidechain in Overbridge. I haven’t learnt the workings on side chain channels yet (and I don’t see it in the manual) but this works. You can send signal from and TO the analog to be processed through the filters and such (you need Overbridge mode selected on the A4), awesome!