I just rewatched season 3 of enterprise, and was looking at the star charts, I think I have a reasonable theory on the delphic expanse location.... it seems likely that both the Briar Patch and the Badlands are leftover chunks of the expanse... you can only screw with space for so long without do some kind of permanent damage, i'd think. so if we assume a sphere-ish shape, keeping Bynaus and Risa out of the expanse, we can safely assume the following star systems were in the expanse:
Gorn (we don't see them till season 4, in the mirror universe)
Part of TNG Tholian Space, but NOT Tholia
and the following Nebulas/Anomalies make decent border markers:
I have my version of the expanse outline in a JPEG of the Star Chart. anyone know how to post it?