This was the only Seas Diamond reference I found:
https://www.diyaudio.com/community/threads/seas-excel-t29d001-had-anyone-heard-it.293222/
I have used several Seas drivers. They are very nice with different sonic signatures. I build and then re-built a set of speakers for a project (2 towers and a center). For the last rebuild, I considered using the Seas diamond, but at $6k per pair, they were just too expensive. I ended up using the Seas Excel T29B001 Beryllium, which were excellent!