Sorry. that was not clear! when i say i connected everything, i mean everything except the screen. in other words, the RasPad has a touch screen that acts as a Generic HDMI device. so i simply moved the Pi, the Zynthian Kit, the HifiBerry and all the dangly bits to the RasPad case/screen.
In the first 2 images below, Zynthian works perfectly, all of the knobs and switches work. However, in the last image it only works headless. adding the MHS35 screen to the official ribbon cable causes the Pi to hang on boot.
does that help clarify the mess i have created for myself?
To be clear, at first i wanted to turn the Raspad into a Zynthian, but i was unable to cram everything inside the case and, honestly, it’s just way more screen than I need. Hence my attempt to get the MHS35 working. This has gotten me thinking however, that it might be cool to package up the sound card, Zynthian expander, and all the knobs and switches in their own box with a GPIO header to connect to any Pi/Screen combo in seconds 
But first I need to figure out this screen issue 