best sub for spendor s8e and 2500 c feet room?

You can go with cheap subs if you don't push them to go down into the 20's. Set them to roll off at 36hz +- and they will work fine. Even expensive and big name subs can and often do sound bad at those low frequencies. Two less expensive subs should sound pretty good and will add a nice foundation.

My opinion here.....

That is a great suggestion.. I forgot about the Hsu's. Heard them at the CES show a number of years ago and they sounded good.