When an amp puts out 90 watts....

I have seen some pnm impedance measures in stereophile that show wide impedance flucuations from 4 to 16 ohms at various frequencies. Far frm the constant high impedance that an amp like that would probably do best with.

The OP's Butler Audio amp is not a full tube design. I believe it is solid state with a tube input stage. Therefore it will not necessarily need a speaker with a flat impedance.

Finsup, It sounds like you are not happy with the sound at present. There are allot of reasons why that could be. If you could explain more about what you're not liking and maybe some details about your room dimensions maybe someone can give you some suggestions.

I have heard from an amp designer that he has abandoned the Zobel because the Zobel network can knock down power output into the higher frequencies and diminish extension. If the speaker efficency is near 96 plus, less of an issue. Have you experienced this? Jallen

ZOBEL networks always have to be set up for a particular situation. Sometimes a choke needs to be in the network to prevent High Frequency rolloff.