The KBL is very good. I used BAT VK5 (not i), but modified with NOS. So I would say the performance is very close to i, only the volume control is different. The KBL is very good, and in fact, much better match with Krell power amp, but we used KSA250, then VK5.
I would say the VK5 sounds too slow. Also, my friend matched the FPB with Spectral DMC20.2, also very fine sounding, although in my system, I prefer VK5 to the Spectral.
Finally, I settled for VK5SE. (not 50SE). VK5SE is probably a good middle ground to have the 3D and slam of 50SE, but smooth and musical of 6922. This is the only preamp that can combined NOS and 6h30 to 'mix-n-match' the sound.