Yeah, that PB16 was a monster, but the S3611 did sound, or should I say I felt the pressure of extreme low frequencies. It was pretty impressive to be a dual 18" driver in a sealed enclosure. It's my first time hearing a sealed enclosure perform that low, with the intensity of a ported box. The only issue I didn't like about the PB16 was port noise, which that's the nature of a ported sub when playing them really loud. Without it, I wouldn't be able to tell the difference. You can feel both models, nor did either distort at high volume levels while responding to low frequencies.
I've been looking for a review by Audioholics to see if they tested these subwoofers.
I wonder if there's another subwoofer at the price point these subwoofers are sold at. The PB16 is $2500 and S3611 is $2000. I was looking to purchase Martin Logan subwoofers. I like their speakers but their subwoofers are not in the same class at all.