I have the opportunity to grab a set of JBL E20's and E30's. Would any of these be a good set? The E20's are rear fire ports so I am worried about port noise on the wall. The E30's are a little large. As far as mounting i can mount any thing with the correct rigging hardware.
I had the JBL E20's and they were amazing small bookshelves. I lost mine in the storm. They would be perfect for surrounds. Try mounting them and If you don't like what you hear you can get some cheap stands on CL or amazon.
I haven't heard them, but afterlife knows and likes them
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If I had to guess, I'd pick the smaller E20 over the larger E30 for rear channel duty.
The E20 weighs 7 lbs, the E30 is 16.3 lbs.
The E20's 5" woofer is crossed over to the ¾" tweeter at 3000 Hz. The E30's 6" woofer is crossed over to what looks like the same tweeter at 4000 Hz. The E20 design makes more sense to me – I can imagine the 6" woofer making breakup noise if it goes that high. I'd worry about that much more than I'd worry about the rear port on the E20 being close to a wall. If you set those speakers to small, feeding them signals of about 80 Hz or higher, the rear port should not be an audible problem.
Energy is a Canadian make that has a decent reputation. Those CB-5's you mentioned should also be OK. To be honest, if you like your front three speakers, finding decent rear channel speakers for movie sound is not difficult. They don't have to be a straight up match with the front speakers. Price, size and weight matter because of what space you have available for them.