I also have a Soundcraft Signature MTK and with the channel trim pots turned to minimum there is no issue taking audio straight from the modular into the desk -- additional attenuation is not needed. Then you can put your effects on a mixer bus or send.
@Lugia -- listening to some SPX90 demo clips.
https://www.vintagedigital.com.au/yamaha-spx90-multi-effects-processor/
You're not selling one are you? I might need the classic sound of "Large Scale Integration" when I start my synthwave side project :) . It is possible I am unduly influenced by the extremely 80s test samples, impossible to be sure.
Latest stuff : https://soundcloud.com/user-352590333