From what I understood, you are looking for a way to input the audio signal of your synths in your scope project.
What you have is 3 (soon 4) hardware synth each with one stereo analog output.
Then you want to had some effects and mix the synth together within scope (and maybe add some scope synth).
So what you need is a solution to get 8 audio signal in your scope board.
The analog audio input you have with your svope project board is only stereo (2 audio signal).
But you also have other digital input with your board (1 SPDIF input and 2 ADAT inputs).
What you need there is a analog audio in to adat converter.
What can be used is:
- SM PRO AUDIO AO 8: 8 analog in to ADAT (156 € new)

- SM PRO AUDIO AO 8
- AO 8.jpg (24.32 KiB) Viewed 2764 times
- BEHRINGER ADA8000 PRO-8 DIGITAL: 8 analog in to ADAT + 8 ADAT to analog out (209 € new)

- BERHINGER ADA 8000
- ADA 8000.jpg (33.14 KiB) Viewed 2768 times
or some more advanced and often more expensive analog to ADAT converter
The "old" creamware A8 (8in+8out) and A16 (16in+16out) would also do the job if you can get a used one.
Another solution would be get you a creamware interface like the A16 Ultra burt then you need to have the "Z-link" version of the scope project (not the "Classic" or the "Plus" version).
Finally another solution would be to add a Scope Home/Luna 3 DSP board + 1 LUNA 2496 I/O converter (this type of bundle cost me 200 € at the beginning of the year).

- Scope Home + Luna 2496 IO
- Scope home + Luna 2496 IO.jpg (13.12 KiB) Viewed 2766 times
It would provide you the 8 analog inputs you need (with cinch type connexion though), 8 analog outputs (also cinch) on the LUNA 2496 I/O.
Then you still have the stereo analog input of your scope project and the stereo analog input of the scope Home for futur use.
And you also get 1 extra MIDI IO in case you need two of them (one is already available on your scope project).
And last but not least you would get 3 extra DSP to add to the 6 you have on your Scope Project.
My 2 cents
CheerZ