@johnnotkathi you can look up the older ESS Performance Series brochures still around on the web (in .pdf) form for download and I found one last night in Denmark (.de) I think it was, for a subscription fee or something to download. Some of these artifacts will list the 9a but not the 9c model.. Same family IIRC but not exactly the same. Don’t hold me to this, but something close to this - 8ohm, 15-75w, 8" woofer, 92db, smaller AMT Heil. Adjustable presence control in front. Some show rear passive radiators. Can be tube friendly, but you’d have to try with your amplifiers. No guarantees, and some of these go for cheap on the used market.May be worth it if you find a set with nice cabinets.
Be careful if you replace the woofer [and don’t re-cone and re-surround it], you may get a larger hole in the midrange on this speaker. Best to ensure something right at 92db efficiency for the woofer, However, I’d try to have to re-coned by Nealsspeakerservice if you can. Best of Luck on the decision, project, etc.