From the website it looks like the Distressor is using balanced analog I/O. I would connect the ins and outs to the XLR ins and outs on the Fireface. The FF Matrix allows you to route the audio any way you want — before the H8000, after the H8000, in parallel, etc. The Eventide does great A/D conversion too, but I find it is easier to route things around with the FF.
In general I avoid effects with analog interfaces. I believe that once I get the audio into the digital domain I want to keep it there until it is ready to go to the amp/speakers. But at the end of the day whatever sounds good to your ear is fine.
