Some very early seat-of-the-pants LX reactions:
As I am unable to perform even a sighted A/B test, never mind a double-blind test, I spent some time blasting the 2EXs today in anticipation of hooking up the LXs. I turned off all room correction / EQ and ran them full-range in Pure Direct. I'm very familiar with the sound of them, and there were no surprises to be found while doing this. They're fantastic speakers, but a little disadvantaged in the compromised space that they're forced to reside in in the family room (up somewhat high and closer together than is optimal). The one and only complaint I have about them is that they sound a bit confined and constrained at times. This is more likely a result of their positioning than of an inherent weakness.
Then the LXs went up (also in Pure Direct) and I performed a quick and dirty level match (the measured difference between the 2EX and LX was between 2 and 3dB). So with of all the perils and flaws of acoustic memory and expectation bias in place and ready to muck things up, here we go...
Yes, the LXs pump out much more bass than the 2EXs do. I was more surprised at the additional mid-bass energy than the deeper extension, which was also obvious. For me, I would certainly still involve subs for music and HT, not only to get that extra bit of extension, but because in this room the speakers reside in a bass null. Hence, low frequency placement flexibility is essential for me. That said, I've never heard so much clean, distortion-free bass output from a true bookshelf speaker. Their impressive performance here should make sub integration easier and more seamless.
Beyond bass frequencies, they do clearly throw a larger soundstage than the 2EXs, which barely changes at all when standing up and down and listening at different points in the room. For me, this was their biggest advantage over the 2EXs. Much of the constrained aspect to 2EXs sound was gone, and what remained I lay at the feet of the compromised placement. The LXs still aren't going to match quality towers in this regard, but the wider dispersion really helps them to overcome the positioning disadvantage. What was also surprising was the effect that this seemed to have on vocals. The 2EXs are wonderful with vocals, as are these, but there seems to be just a little extra dimension to them with the LXs.
Now we come to the RAAL ribbons versus the Titan dome tweeters. As far as speakers I've recently owned, I'd rank their tweeter performance as follows, starting with the best:
Sierra RAAL towers
Sierra 2EXs
Revel F226Bes
Emotiva T2+s
My acoustic guitar benchmark tracks are Keith Don't Go (Nils Lofgren) and Poor Lonesome Me (Eugene Ruffolo). Honestly, without the benefit of A/Bing, not much about the Nils Logren track stood out as clearly better or worse. I think maybe the LXs lose just a little bit of precision and texture, but I can't say for sure going by memory alone. This changed with the Eugene Ruffolo track. I am very, very familiar with this song, to the point that whenever it's on my wife somehow appears to say, "Oh, testing speakers again, are we???". The opening high-notes of the guitar are pristine on this recording. When listening to this on the RAAL towers, it's seriously like there is a literal guitar being played right next to me. There is nothing missing. The 2EXs come very close to achieving the same effect. The LXs...sound really great, but don't quite hit the surreal level I've heard from the RAAL ribbons. The LXs actually reminded me almost completely of the Revel towers in this area, which is certainly not a knock on them as they sound great as well, it's just not quite the same as the ribbon speakers. At this point I'd put them on par with the Revel's Be tweeters in the list above.
Anyway, lots more listening to do after rolling in the subs and EQing.
