So I got home and busted out some Costco yellow towels. I plugged both the ports on the S60 towers. I ran Audyssey for a quick 3 point to see if it worked. Checked the settings and wam the deep valley was gone. oh yes. So I ran Audyssey again for the 6 point test. Freaking fridge kicked on in the middle of the test. so the left speaker is dipped hard on the lower end but comes up quick @ the 80hz mark. see attached
Audyssey set the speakers to small and crossover @ 60 with the towels in. I changed them all to 80 played some U2 it was nice and clean no boomy bass. Did the GoT battle for black water and oh yeah it's sweeter than it was.
The hollow sound is now gone.
Room is a totally open layout stairs, halls and kitchen.