I have only read that the Klipsch Belle speakers are not known for their deep bass. I do not even believe the Belle is capable of going to a "reasonable 30 Hz." I think the Klipschorn and the Cornwall can get pretty darn close to that. I am thinking long and hard at selling my JBL L300 Summit speakers, or swapping them for a pair of vintage Klipschorn speakers. I think you are asking too much from your Klipsch Belle speakers to get down anywhere close to 30 Hz. Try to audition a pair of Cornwall speakers. I have heard these and they sound quite good with SET amps.