Tracy,
Dolby Labs bought SLS several years ago and still sells some product with their drivers. They MAY offer support for older products. You could try that route if you need replacement drivers.
The PRD500 and PRD1000 ribbons used in most of SLS designed were custom units designed by none other than Igor Levistsy. I met him at the SLS audio booth at an AES convention and he described the drivers in great detail to me. They may look similar to other cheaper, readily available planar drivers, but are of a much higher specification. If you've ever held one, you'd know what I mean. They are large and heavy and very well built. That being said, when SLS need smaller fill type speakers, only requiring more limited output, they did use some variations of the Neo3 style drivers. I'm not sure how different they are though, in terms of trying them as a drop-in replacement.
Greg
