In your case the 218 would be the endpoint for streaming. You would choose between the two via your control app. If you find it easier, you could disable the MC200 player so that the only endpoint would be the 218. The side benefit of keeping the two endpoints active would be that you could do direct comparisons between a MQA track that is played via legacy equipment versus MQA being completely rendered to SE speakers.
It's quite messy though, no? You'd want to stream to the MC200 --> G65 to apply DSP and room correction with non-MQA material, and to the 218 for MQA material. The latter route doesn't get DSP presets or room correction.