JBL's by design have sonically tight bass because of it's studio lineage. Some say the bass is dry and some say too fat. I had good luck using several tube amplifiers. For instance VTL ST85 had tight bass for a tube amp. My Dyna ST70 dis a very good sound too. You might try a hybrid amp like a Pathos hybrid amp. There are others but this sits at the top of my list. I also like the Moscodes too. Your JBL's don't need alot of power. Also you must know your product upstream too. Sometimes they can change the character of sound.
