I went through this a couple years back and ended up buying a VMPS 626R for use as a center. This is vertical monitor, and I turned it upside down, with tweeter at the bottom to attain tweeter and mid-panel orientation to the ear. The angle was still very steep, and care should be taken in trying it. I used a Lexicon MC-1 for a processor and set the center cross at 120 hz and the 645's at 80 hz. The VMPS could have been set at 80, but sound quality and imaging was a better match this way and was quite enjoyable. My 645's were not modded. VMPS did not have the razor detail of the Newforms but the VMPS was very, very smooth right out of the box,with excellent clarity and very natural presentation. VMPS does have a dedicated ribbon horizontal center now, the LRC. VMPS has a limited number of dealers. Possibly you live near to one or VMPS can suggest how you could audition one. Good luck on your hunt.
Regards,
Will
Regards,
Will