I too have upgraded to the Treo CT model with the carbon tweeter and the robustly constructed cabinet. It's just music now. I don't even think about individual drivers. Everything is "of a piece".
I haven't had the pleasure of hearing the 2Ci vs. 2Ce Sig. but knowing how Richard is always working toward an increasing level of musicality in his designs, I would imagine the most recent iteration of the model 2 will be superior in musicality.
Best of luck to the OP. I hope you can audition the speakers in your system and your environment. Looking forward to the results!