Bentley Acoustic Corporation EC86 Tubes?

Just heard back from Acoustic Plan, I can use EC86, E86C or EC806S tubes from any source. They confirmed that BAC tubes would no longer be available. They also said that it is important that the tubes be "matched to a quartet".

Do you know or can you suggest a source that will describe the expected sound differences among the three tube choices?

BAC were importers and rebranded other manufacturers tubes. Consequently, it's difficult to say how good they are. However perhaps the designer picked these as a known best quantity from a NOS stock. The EF86 is very cheap and available. Why not roll in some other makes for comparison?