I'll chime in since I spent more time than anyone comparing the E3 and SS8 at CAF. I went there just to try an decide which will be my future upgrade to my HT2-TL. The effect of auditioning the two of them left me with more to think about than I had hoped. So get ready for wall of text.
I love the sound of my HT2-TL. They are smooth and detailed with almost magical sounding soundstage. My problem with them has been the natural looser sound of the low end of transmission lines. I wanted to get soundstage that would seal up that loose low end and keep the smooth and detail presentation. Transparency is priority to my tastes. With the hype around the E3 bass and word of the magically sounding mids in the Exotica drivers, I had to listen to it before jumping on the SS8 bandwagon.
First off, I'll say neither the E3 or SS8 is better than the other as an overall package. Both speakers are revealing and detailed. They are more or less capable of giving you just about everything in the music. The difference is the way they present this sound. The only thing that is definitely better is the bass on the E3. It is clearly tighter and faster. Yet, the SS8 is so good itself you would never even think about the difference if you didn't get a chance to compare them.
The SS8 are much better at the disappearing act. The imaging and holographic sound stage is there, but the speakers are not. The SS8 remind me more of my HT2-TL than the E3. It was closer to what I imagined I wanted to gain from upgrading my HT2-TL. A very smooth speaker, from top to bottom, but doesn't give up tight bass to accomplish that smoothness. The smoother sound of the SS8 sounds more like it is a single driver than the E3; a characteristic I consider more appealing for intimate listening.
The E3 I consider a louder speaker and I am not talking about the sensitivity. While it has tighter and slight deeper bass, the mids and highs do not sound as holographic as the SS8. The Exotica drivers do things differently than what I have heard in other drivers. But what it does, it does very well. I found the effect of the Exotica drivers to be surprisingly engaging in the vocals. The vocal tracks are what I found most attractive on the E3. I found the combination of the tight bass and engaging vocals presented a more "I'm here" presence as opposed to the holographic smoother sound of the SS8. If you love vocals, you should will likely find bias towards the Exotica drivers.
Keep in mind what I said above. With the exception of the bass, I do not think either speaker misses a beat. They just present the sound differently and paint a different picture. If I were to dumb it down to a nutshell, I personally, would consider the E3 something akin to a rock concert (I don't mean this in any negative fashion) and the SS8 to something of a live orchestration. I certainly preferred the sound of my orchestrated tracks on the SS8. But Lana Del Rey's voice on the E3 was giving me mixed emotions.
Something I want to stress here, is that I would never know any better in regards to "what ifs" between these two speakers if I never had a chance to compare them side by side. I had a lot of mixed opinions comparing the two only because were side by side. If I had just listened to one of them without the other, I would have been perfectly content with what I was hearing and not question it (Both are everything my HT-TLs are and then some without the loose very low end bass that has become a slight displeasure to me). They are both so good at what they do, I don't think anyone would think about "what ifs" if they had one in their house and never spoiled them self by listening to both in the same room.
Having heard and understand the difference in both, I began thinking how I could get the best of both worlds (Much like anyone would). I talked to Jim a lot on all sorts of alternate concepts. Using the RAAL on the E3, using servo on the SS8, etc. Everything came with a condition. But since everyone is probably going to consider them anyways, I'll list what Jim and I discussed.
1. Using RAAL on the E3 is easily doable but might ruin the magical that combining the Exotica drivers gives. Regardless, I think this will likely crater more to my personal listening preference
2. Servo drive in the SS8 cannot be done with the current accuton driver because it is crossed at 500hz. Jim, mentioned a larger, high sensitivity accuton that might work with a servo driven design. But that would come down to how low the larger driver can be safely crossed over with enough headroom that the ceramic driver will not shatter from louder listening levels. I don't know if Jim would consider this a safe design in practice.
3. Using a scanspeak woofer instead of the Exotica. This should give a much smoother sound like the SS8/HT-2TL that I love and bring back the single driver feel while besting even the SS8 in the bass. But the sacrifice for this design would come in the sensitivity. Jim says the illuminator would come down to 83db-ish once implemented. Being as I have two highly capable monoblocks, this combined with a RAAL is an option I am actually considering. Although, it is a huge leap of faith on the presumption that will it live up to my expected presentation.
There are probably other designs options as well. I personally think the custom torrent driver Totem Acoustics designed for their element series would be the ideal woofer for this application. It has the clearest sounding mids and I ever heard (it is designed to operate without a crossover) and is high sensitivity with incredible power handling. Unfortunately, obtaining them would mean buying a $6k pair of monitors and ripping them out as they will not sell the drivers alone (Yes, I asked them). And that is still a risk since the design might not even work out.
If anyone want to take a plunge on an alternate design, please do #3 first for me and report back here immediately.

That said, if I were to choose between the two speakers are they are, I would personally take the SS8 and save $4k on the base price. That would net me a huge budget for equipment upgrades or even more Vinyls/CDs to listen to on my new speakers. As much as I love Lana Del Rey, I probably listen to more orchestrated tracks and other vocalless material.