Yes - The PB-10 is an excellent sub and two would be even better but they are no match for the PB 13 Ultra.I assume that means there is still a massive difference.
With either option, EQ would be a must to enable the best performance. Have you taken that into consideration?Which would offer the most in performance, buying another three PB10's for second hand which would mean I would have 4 PB10's or one PB13.
Space is not a issue. Cost for both options works out to be the same.
You could use Russ' infamous rug/blanket method. Underneath, of courseRuss, thanks for that lenghty insight. I've just discovered though that the PB13 weighs a massive 70KG's!!!!!!!!! I thought it weighed somewhere between 30-40KG but 70KG is just insanly to heavy for me to start lugging it about in different postions. And to think I was even contemplating getting two of them if I were to get one.