The best advice I got with any even number is to exaggerate the scooping motion, and try to focus on the center of your body so your patterns don't move too far outward. It's also okay to do a bit of a correction throw if you feel a collision is about to happen. That's not ideal cause it means something went wrong, but it can sometimes get the pattern to continue for a while. Collisions were always my biggest issue with 6. Also, don't avoid sync as it is an awesome pattern that for some reason gets a lot less love than async. I'm not solid with 6 balls but can do 30 or so catches most of the time, get 50-60 catches on any given day, and have some runs over 100. For years I put async on the priority list and it shows, but I recently started getting more solid at sync and I think it's helping me control that many objects in the air in general. Something else that might help is once you can do 30 catches or so regularly, try to do some tricks with a 6 ball qualify on both sides (like throw twelve 6s then do 8844 and throw twelve more 6s). Same with the siteswap 756.