Thanks so much for your response - I went and checked and the aggregation was reversed. So I fixed that, and within Studio One, all is happy as far as the internal routing goes.
Interestingly, my PC Sound output device still reads "Main Out (2- Presonus Quantum)" and selecting that is the only way I can get sound coming out of my master Quantum (now aggregated as 1 as well.) I am not experiencing any adverse side effects other than the OCD side of me is not happy with all the labels being the same... I'd be happy to hear any other ideas of you have them. Thanks again.