This reminds me of when I had two Roland Mobile Cube Battery-Powered Stereo amps. Though it is a stereo amp, with speakers right next to each other in such a small case it didn't really do much in terms of stereo. That was until I connected two of them in stereo. It sounded so much bigger and better that it shocked me. So
I understand exactly what you are saying.

I'm thinking for myself; if I were to have a setup similar to 2 S1 Pros, what alternatives would I have as I try to avoid having to buy Bose and Apple products? The Aiwa Exos-9 comes to my mind. There were quite a bit of discussions about it on this forum and I know that some members are using them for gigs. Two units can be connected wirelessly, which is cool. I meant to buy two, but didn't have an immediate need to do so.