I'll try my best to explain the differences in what you would hear. After listening for the HT2-TL's as long as you have, the first thing you would notice with the Song3 Encores is that they sound like a much larger speaker (they are larger). That is because the Satori 9.5" woofer can move much more air down low. So from a bass perspective, the Encores are hands-down winners in this area.
In the midrange, the the Audio Technology mid (basically a Dynaudio driver) is a bit smoother and warmer sounding than the Seas Excel W18's in the HT2-TL's. This is always a balancing act. Some people love the incredible detail in the Seas W18's. Others may find them to be a bit too "analytical" for lack of a better term.
For many years, I preferred all the detail I could get out of a speaker. That is because I worked in recording studios and wanted to hear every minute detail in a mix. But I find the smoother performance of the AT mid to be very relaxing and can listen to it for hours on end. In a way, it is like the difference between a good tube and and a good solid state amp. Both can sound great, but they definitely sound a bit different.
As for the tweeter, I find the Beryllium tweeter to be as detailed as the RAAL ribbons in the HT2-TL's, but with superior off axis response (since it is a dome). We have never used a metal dome tweeter until Be tweeters came on the market as they can tend to be a bit edgy sounding. But there are two positive things that make Be a good choice for a tweeter.
First, unlike other metal dome tweeters, the cone break-up mode of a Be cone is 34kHz...well beyond audibility. The second advantage is that they are self-damping. So instruments like cymbals don't hang on artificially like they can with other metal domes.
With those two advantages in mind, I think the top end of both of these speakers would rate about the same.
As to your question about placement, the Encores are front ported. So they are about as easy to place as the HT2-TL's. We have played them at audio shows with great success where the rooms tend to be about 13' x 19' or so...not large. With a large woofer, the bass will tend to "pile up" in corners and against the rear wall. But if your listening position isn't near these, you will have no particular issues. If you need to be near the rear corners or wall of a room, you can use bass traps to deal with this. Either way, I don't see room size as being a major issue.
- Jim