rosami,
I have extensive experience with the 3.7 and 2.7 and the older big CS6.
I am betting that the thinness you heard was very likely in the set up of the speakers. As with many speakers, I found I could dial in the size and richness of vocal and instrumental tone and images via tweaking speaker positioning. If placed closer together, or if toed in a bit too much, it could squeeze the sonics down. Once I had my 3.7s dialed in they sound was HUGE in every way, and extremely big and lush.
I originally thought I'd have to live with some level of disappointment with the smaller 2.7s due to a reduction of "fullness" and size to the sound.However, like the 3.7s, further experiments in placement in my room finally yeilded the type of big, rich presentation I was used to from the 3.7s.
Of course, I can't tell from my perspective that your 3.6s actually *don't* sound richer and less thin than the 3.7s. It's been a long time since I heard them myself, though my memory is that they sounded thinner than what I got from the 3.7s. But the 3.7s definitely sounded richer than the CS6s I had.