Oh that sounds like the official SuperCollider stance might be that any use of scsynth from an existing project via the network OSC API is considered an aggregate. Is this the case?
I definitely don’t want to create any issues and it would be great to get some clarity here.
I don't think that the SuperCollider team has an official stance on this and I can't really speak for all developers. Legally, I think you're on the safe side as long as scsynth runs in a separate process (which is the case for Sonic Pi). However, it's probably against the intentions of James McCartney. If he had wanted scsynth to be used by non-GPL programs, he would have released it under the LGPL. But that's just my assumption. If you're in doubt, just ask him :)
also keep in mind that the gnu.org want gpl to apply as widely as possible. Generally, your approach should be fine imo