From the curves of the CD and horn together, it looks as though you need 10dB of attenuation. I'll keep looking. Yours is a common combo.
The horn is clearly 8 ohms based on the OP's model # and the linked spec sheet.
The woofer enclosure is listed as 8 ohms on its spec sheet so if the woofers are 4 ohms each, wired in series, the overall cabinet would be 8 ohms?
The woofers are wired to 4ohms in these.