Hi Martin, I have found a pair -- thank you. I'll take down my wanted ad (I had forgotten about it).
Quite a while ago the foam on one of the woofers decomposed and I went looking for a replacement. The local stereo shop had a 10" KLH 4-ohm acoustic suspension woofer that fit perfectly and sounded just like the original. Maybe it was of identical manufacture: I know Rectilinear didn't make any drivers themselves; I don't know whether KLH did or not. So it may not be too hard for you to find replacements. Since the crossover is 100hz, all the woofer does is real bass, and I'm sure 10" acoustic suspension units are still out there.
I never blew a midrange driver on either pair I have. I think the model may not have sold well since it was in direct competition with Acoustic Research and their entire line of acoustic suspension speakers. AR had a great reputation; maybe anyone who wanted that design just went to AR.
The Xa had a slightly different crossover than the X. No other change.
I bought these after living in Boston for a year and going to the Boston Symphony as often as possible -- I was in the Coast Guard and, as active-duty military, could go to a concert and, an hour before the concert, buy any unsold ticket for $1. When it came time to buy a stereo, I bought a few records (vinyl) of the orchestra, recorded in Symphony Hall, famous for its acoustics, and went to stereo shops. During the week in the middle of the day they weren't busy and they let me listen a lot. These speakers really stood out for their resemblance to live performance. I was surprised -- I'd thought several brands and models would be about the same. Nope, and I haven't heard more realistic speakers since. They're still going strong, and I just wanted the second pair as backup. You should be able to fix yours easily. Please do -- they're one of a kind.