The LGK 2.1 and X-LS are more similar, they are voiced to be balanced, but they do have some thing differences tonally that measurements wont show.
Using a wide-band instead of a traditional tweeter offers a really cohesive sound, that is really tough to beat, especially when it comes to midrange, especially vocals and acoustic instruments.
Where the Encore's win out is in bass extension & texture, especially below 200Hz, and also in upper-treble clarity & detail due to being a lighter weight material, but for us we don't really feel like we're missing out, especially if you have a good sub. The LGK models will likely sound a little more "smooth" compared to the Encores which are more detailed and "clear" up top.
The 2.4s are likewise very similar to the smaller 2.1s, with with the main differences being 4 woofers in series vs one. The 2.4s also have a 2nd set of LGKs as rear ambiance driver which gives them a greater sense of space & openness, especially in the treble. (something we also did with the old LGK 1.0 "Skinny 6" model)
The Midrange and treble of the 2.1 and 2.4s are pretty much identical, except for the more spacious soundstage in the treble. The rear driver only needs 1 foot of space behind them.
Bass isn't too much different either, only a little deeper than the 2.1 at 60-65Hz depending on placement, but the sealed design allows for more flexibility with placement & makes it easier to control room issues.