Ha, you are right - I can't find reviews either, in fact all I found when searching was this post of yours. I THINK the HT-C6900 is just an update of the HT-C6500 - adding 3D functionality (which means HDMI 1.4) and wireless rear speakers. That might explain the lack of reviews.
I'm considering buying this blu-ray surround sound system from Samsung, but was surprised to find a complete lack of reviews for it on the web. Anyone know why that would be? It's been out since June. Anyone have any opinions on this system? I'm especially interested in knowing how the sound quality on this compares to the HT-C6500.