Which Speakers?

I have a Sherbourne Amp

Where you sit, where the speakers are, and what acoustic treatments you use are all going to have a _huge_ effect on what speaker works best for you.

Much more than the room size.

I've been swapping out a variety of speakers for the L/R in my HT - Reimer Teton GS (giants) w/no center, Paradigm Ref Studio 100's with Studio CC, Odyssey Nightingales, and finally my Merlin TSM-MX's w/o a center channel. Contrary to what I would have thought, the little Merlins used as "large" with "phantom" center are by far the most coherent of all of them, especially for dialog. I presume that's because they are essentially point sources in that mode. I wouldn't try them with a cheapo receiver, but in my Arcam system they work really well. And of course, for music, they are terrific. I have 2 ACI Titan II subs as well, so the foundation is no problem. If you go with any of those brands I'd suggest staying with a "small" 2-way like I did if it works out to integrate the sub for music. My family members actually demanded I put the TSM's back in the HT after swiping them for use in the separate 2 channel system.

IMO, you have already picked 4 very good brands. I would suggest you continue with Thiel just for continuity and whatever synergy it may bring. What type of amplifier do you have?

Agree with Unsound. Theil will integrate better then another brand with what you have.

The Thiels seem like a natural considering your already using them for surrounds.