I thought the CB was alright, one of the better ones, particularly for closed-backs.
I think the OTL people were referring to ones with high output impedance. I've heard of low output impedance OTL like the EC ZDS. If the output impedance is like BH crack's, 120 ohms, and since planars are lowish impedance typically, they will not get enough power to be driven properly that's all. If OTL can deliver sufficient power, that's all that matters.
I don't find upper-mids recession causing bigger sound stage, there are other physical aspects involved in the tuning to cause the larger soundstage. Upper-mids recession is just terrible tuning, that is all. Everything is in the mids.