I replied to your similar thread over on Audiokarma.
I don't think safety caps for the HF driver are as important when active biamping with a tube amp, since you have the OPT's to protect the drivers.
When I biamped with SS amps, I did use something around 50uf. It would probably be the safe way to do things regardless of the amp choice.
I'm curious about the little box that the horn is mounted to. I would think that would cause some reflections.
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