I see this is a somewhat old post, so let me know if you have already solved the problem. I don't remember the exact values we used, (the Model 8 pre-dates my time at Sunn), but I think we just used a resistor and cap in series with the horn driver. I THINK we used a 16 ohm RCF compression driver , but not positive. If you can read the info off of the driver, I can give you some values of resistor and cap that should work fine. I'll respond quicker if you send it directly to my email, rather than posting it here...I might miss it. Let me know.