Are you sure the quads were being driven to their full potential?

In another post, I calculated the input impedance of the 600 to be 43% of the output impedance of the pre/pro. I found out later that the output impedance of my Denon is 10K. That puts the 600 at 4.3K. If you had 4 connected, that's an input impedance of 1K.

Do pre/pros out there drive loads as low as this? Maybe JohnK can jump in here who knows more about system specs than I ever hope to know.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated