Anyone know the Shahinian Diapason Ensemble????

On option would be to contact Bill at Millersound and see if he can rebuilt your passive radiators.

What is confusing is if you can purchase the radiators new for $20, why not just purchase 4 new replacements and be done for $80?

Why not call/email Shahinian?
They are still in business. You can also question them on the cost issue while you are at it.
It seems a fair question, but there might be reasonable answer.
B

I have always enjoyed the "presentation" (sound stage, imaging) from omnidirectional speakers. I am familiar with the various permutations the Ohm line, and I was a dealer for Larsen speakers for several years. I am still enchanted by my Shahinians. I think they sound closer to live acoustic music than any other speakers I have owned or have significant experience with.

I recently purchased the Hawks because, as much as I enjoy the Obelisks I wanted more. OK, I'm greedy. I imagine that your  Diapasons will provide even more goodness. What size room are you placing them and how are you positioning them?

Another reason is that I really want to biamp these speakers, which isn't possible with the Ob 1s. My Hawks need to be restored, so they will be going to Long Island shortly. But my tests so far indicate that the top cap (midrange and tweeters) is less efficient than the woofer in the bass cabinets. So my initial idea of running a moderate (40Wpc) tube amp on the top and a SS amp for the bass cabinet may not work out as planned. We'll see after they come back from restoration.

My room is 25 feet long, 15 feet wide, and has a 22 foot high ceiling sloping down to 18 feet.

I am messing with the placement now but it is much easier with omni directional speakers.

I’m running them with a Bedini 150 MKII amplifier now but will set that to just the bass and run the top with my GM70 SET amp as soon as I get my active crossover back.

Two months later, any progress with your Diapasons?

I have a pair of 2014-vintage Diapason 2. In addition to a larger "Double Eagle" bass cabinet, the passives on this series were changed to a standard looking poly cone design with rubber surround. I haven't pulled one yet to see if it's internally weighted in any manner. No need, I have no concerns about the bottom end.

I gather yours are a version of the original design, with the passive having a ribbed cone, foam surround and washer glued onto the dust cap. I'd be more wary of replacing those types with generic passives than I would on the newer ones like mine, if for no other reason than the ribbed visually look quite different to anything else out there.