- Load an External Effect from Devices>Effects>M/S>External Effect.
- Open it, and select an available ASIO input and output, for example to an input channel of your sequencer which throughputs to an ASIO source.
- Save the external effect with a new name on another location, for example in the project folder or in the Devices>Effects>M/S folder.
- Load the newly saved external effect anywhere you want now: in an insert slot of mixer/synth/modular, in straight the project. Why not as an Aux effect on the main mixer?
The same can be done for hardware IO and effects - without extra latency since that doesn't use ASIO. I always save a special External Source for hardware synths, External Dest for my main mix etcetera. These I save in the Devices>Effects>M/S folder: when I later have the stuff connected to other hardware IO, I just edit the External device and re-save it. As a consequence, all old projects are suddenly compatible with the new hardware connections, without having to reconnect every single one of them throughout the project.
For more info on the External Effect, read the Scope documentation!