Thanks for the input guys. The low efficiency doesn't concern me too much. I'll be bi-amping with an NAD amp on the woofers. It's plenty beefy and has a variable level control on the back, +/- 6db I think, which should allow for matching up the different efficiency levels. Plus, I'll be using a Behringer 2496 EQ on the bass amp for room correction, as I do now with my bi-amped VR4jr's. Work's beautifully, and will allow another way of balancing loudness between drivers. In fact, if I do decide to buy the BG planar ribbons, the first thing I'll try is sticking them in a panel (or cabinet) on their own and using them with the VR4jr bass cabinets. They put out beautiful bass from 23-250hz - might be a nice match with the ribbons. I know it wouldn't be a true line source and would have some issues, but it'd be an interesting experiment....