I also owned a pair of of 645s. I did expensive crossover upgrades and I still didn't care for them. I think my room was too small for the ribbon and bass to integrate right.
The ribbon sounded great though (maybe too fast for my taste the woofers couldn't keep up) I though it has good bass extension also.
I now own a pair of Eminent Tech. 8A ( will do the tweeter upgrade to 8b when funds allow). I enjoy these speakers much more. (the tweeter is not as clean fast the Newform - which probably will be alleviated with the 8b upgrade). They go lower and are very coherent. Not pretty to look at, but neither were the Newforms.
The ribbon sounded great though (maybe too fast for my taste the woofers couldn't keep up) I though it has good bass extension also.
I now own a pair of Eminent Tech. 8A ( will do the tweeter upgrade to 8b when funds allow). I enjoy these speakers much more. (the tweeter is not as clean fast the Newform - which probably will be alleviated with the 8b upgrade). They go lower and are very coherent. Not pretty to look at, but neither were the Newforms.