Thiel replacements

I've sold/owned Thiel's for years. What you have MAINLY, is an acoustical/system setup challenge!....I garantee it.
You are dealing with what so many (ok, most) people deal with every day. Their setup, speaker and seating possition, and their relation is the main and foremost problem, from a foundational standpoint. That and their acoustics overall in the room are not effective to that set up either. Added up, improper speaker, seating, and acoustical treatment considerations will give you AWEFUL SOUND EVERY TIME! From what I'm assuming from your description(although you didn't specify ceiling and floor situation, or sidewall/back wall/front wall specifics), you have some major challenges(the room, setup, speaker, seating placement, acoustic treaments, structural challenges, calibration/tweaks are easily 2/3's the battle sonically!...no joke).
Your room is not 13x18 if you have no left wall, which opens up to the next room(how big is that connection/opening/doorway/whatever?). Your room is acousticallly much bigger, and your dimmensions acoustically are differnt.
How high is your ceiling? What's on your floor and sidewall (right speaker), back and front wall?...bare?
As it stands, you have different(likely radical) frequency response for your left speaker than your right(and vice versa). The right speaker is getting a likely double reflection back to your ears immediately after your direct response from the speaker. This blures and softens image, obscures detail, etc. Your left speaker is more out in "open space", and is giving a differnt signature than your right speaker. If you have a low ceiling, and sit back a ways, you will also have to deal with another reflection issue, with similar affects (assuming flat ceiling).
You couple that with reverb issues, other reflection(non-treated surface) issues, room modes, balance issues, etc, and you have problems.
I bet if you took your same gear, and put it in another room/setup, and you'll get different results!...assuming better setup.
If you can't switch your set up around, and address acoustics issues, you will only go so far with ANY SYSTEM!
Good luck

"double reflection"...I'm sorry, this is a mistake. I mean you're hearing a "double image" with the reflected info(assuming bare wall next to your right speaker) coupling with the direct sound from your speaker back to your ear! If left unchecked, you will hear a smeared less than accurate sounding image. Your left speaker may be giving differnt results. HOwever, if you are getting an image off of your left wall between you and your "6' opening", you will have same problem there. And yes, the opening is affecting the response and imaging of your speaker. But, the right wall is giving other problems being next to your speaker untreated. Really you don't want any reflective surface right next to your speaker mostly. This has some sonic consequences/challenges.
Also, the opening behind your chair is a challenge.
"Master Handbook of Acoustics" will tell you (as with many respected acoustical engineers (consult Russ Herschelmann, Rives Audio, PMI, etc) that putting speaker and chairs infront of "opening" to other rooms will cause some strange response issues in your sound. This must be considered. Basically, you want even and "flat"(or close as you can) response from ALL speakers from your listening possition. This is a major problem with your likely "less than ideal" set up. You'll also have to adress the "first order reflection points" (including ceiling if you dont' sit close enough...which is a problem with Thiels, because they are simple 1st order 6db crossovers, which need room to build) .
My suggestion, change things around or you'll have limitations. Using onother set up or room might be your best bet, even if it means smaller speakers. The room and setup is over 50% of the performance. You need to know what's going on.
Also, from your description, I presumed a flat 8' ceiling. Sitting back too far also adds some challenges to for you with those speakers!
You might want to tinker with these speaker in a nother set up situation to compare. Good luck. Better yet, email www.rivesaudio.com and pay for a consultation/room fix! Otherwise, you can do what many do, and that's go through gear to no end, and you still have a poor room setup problem!!!(you must single handedly identify your "culprits"). ex