Springbok, yup it's just like Al said. Take a look at some of my posts which discussed how I loaded my ARC Ref 3/5 preamp's 2 outputs: Main 1 -- drives the main amp. Main 2: -- drives a single subwoofer. ARC recommends that the combined load impedance presented to the Ref 3/5 NOT be less than 20K Ohms.
Using Al's formula, I realized that I overloaded my preamp. In my case, I found a gent who custom designed a built a buffer device for me that presents Main 2 with a much higher impedance load. The device also (i) sums the left and right channels for the subwoofer without shorting the Mains and (ii) enables me to tap both loads into the preamp's balanced outputs.
It's a cool device and was NOT terribly expensive.
Using Al's formula, I realized that I overloaded my preamp. In my case, I found a gent who custom designed a built a buffer device for me that presents Main 2 with a much higher impedance load. The device also (i) sums the left and right channels for the subwoofer without shorting the Mains and (ii) enables me to tap both loads into the preamp's balanced outputs.
It's a cool device and was NOT terribly expensive.