I just got a new pair of KRK monitors with a 5" woofer. They are making me miss extended low end of the Yamaha HS-8's that I elected not to rebuy due to the $$ difference...I like everything about these KRK's except the less low end. I'm in about a 20' by 15' or so small room...KRK makes sub-woofers, what size would work best with the monitors? Interestingly, there isn't a cutoff frequency knob on the back of these, so I guess they will have to get full range....also, assuming the sub has a cutoff frequency knob, where should that be? These are KRK Rokit 5's (in a super snazzy chrome finish)