You can get plenty of support by anchoring to the wall. Find the studs in the wall with a stud finder. Cut a large enough piece ply wood to span 2 studs. You can make the plywood look nice by staining the same as the JBL cabs or paint the same as wall and it will blend in. You can then buy large Corbels for a shelf or make your own that angles down.. Attach to the anchored plywood on the wall. Or buy one of many various swing arm monitor or tv support devices. You can fashion a shelf that will attach to a swing arm. Just remember the whole thing is only a strong as the connectors. Even if you get a heavy duty swing arm it still needs strong connector. So use lots of long wood screws into the wall studs to anchor plywood. Adding a couple molly's would not hurt. Use a lip on the shelf for security. I would suggest a small wire attached to the speaker in case of quake... a little would putty would repair it so you never see it. Ok that is the DIY wall way of doing it...
If I was doing it I would do a plywood anchor to the ceiling and install omni mounts to the speakers. Just remove the woofer and drill holes and bolt through the JBL cabinet. Here is a link to the omni mounts and some pics of what it looks like. It's the best way imo....
https://www.google.com/search?q=heavy+d ... Yd3-aZM7M:
Looks like this....
