What brand and model are your monoblocs? My Classe is 400 into 4ohms and works very well with the Thiels and my Connie. I'm quite happy but every time I hear tube amps in another person's system, I'm beguiled. I guess I'd like to introduce a little more tube magic into my system without losing the bottom end grip. I'll never forget going to a tube preamp for the first time. I'll never go back to a solid state pre. I agree that power is critical with the CS 3.7's....which is why tubes might be out of my monetary reach.
I may have a chance to audition some NAT Generator monoblocs but not for a while. They're push/pull 275 wpc into 4 ohms.