I hesitated to post "yet another Sierra-2EX review" because of the excellent posts like those by theophile and SunByrne, but what the heck, this is sort of like telling your friends you too found the new favorite ice-cream place.
Executive Summary: If you are considering the upgrade from Sierra-2 to Sierra-2EX, do not hesitate. This is not a minor tweak, and I believe it to be 100% worth it.
I was going to do careful A/B blind comparison tests so I could legitimately support the executive summary of this post, but when the upgrade package arrived, I couldn't help myself. I immediately did the upgrade, then strategically waited for my wife to leave the house before "the test run".
Jennifer Thomas' "Flight of The Phoenix" has some great low horns (think like fog horns) that were a great exerciser for the new woofers. Lovely, nearly goose-bumpily. If you have a quality audio source, these speakers simply shine with musical content.
Movies: check - The Greatest Showman and Spiderman Homecoming were next. Sound effects and music tracks sound great. I have a 5.1.4 setup with 5 Sierra-2EX speakers in a large acoustically challenged basement room. But the home theater experience was excellent. Not once did I need to crank up the amp to "11" in order to get the fullness that I am after.
Streaming - Sounds silly but I streamed Disney's new Turner and Hooch and found myself immersed several times in the audio track, like in the opening credits and a few spots during several episodes. I would catch myself realizing that the sound was just so good.
I am curious about what some of you have used to exercise/test/demo these speakers...
Final Impression: When I first read about the 2EX upgrade, I was concerned it might be minor and incremental. However, even without my "scientific" A/B blind test, I am convinced the upgrade was well worth the effort. I can't believe sound this good, clear, and full comes out of a box that size. If there were a prize for best sound per cubic inch, these speakers would have to win hands down.