Jason's right. But I blame myself. I should have known better and asked the question on input impedance before I bought it. I can't beat myself up too hard though because I could have never imagined that the 600's input impedance would have been this low. It's rather unusual.

I suppose this is one way of ensuring that the receiver output can never saturate the sub .

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