I don't own the JRs but own the SR MKIIs with MC501 monoblocks and can say without hesitation, no subwoofer necessary! The bass response is indeed very dependent on the speaker position. I have the about 4' from front and side walls and slightly towed in (room--16'x30' w/10' ceilings). The bass is deep and tight and imaging is tightly focused but throwing a huge soundstage. Not sure how Albert "mad scientist" Von Schweikert does it but all of his speakers are magical. A friend just today bought a pair of the JR MKIIs and they no doubt will be great in his system. Have fun enjoying the music.
