I was curious how you make them as well. I've asked the creators on the ones on the market and they won't share that knowledge. And it isn't as simple as a root prim needs to be on the sim. there is the linking distance limitation.
These sim surround makers, i see ONE root prim on the sim, then the distant sim surround 200 meters away.
Plus isnt there a size limitation on uploading mesh? like 64x64x64? I see most of these surrounds quit a bit larger than that.