Equipment cannot gaurantee sub-50Hz bass. The key determinate of high quality deep bass is the interaction between your room and your speakers. Speaker/listener positioning is critical as well as appropriate equipment isolation from feedback. Somewhat paradoxically, subwoofers work best with those speakers that need them least. I take the position that subwoofers shouldn't be used to provide bass, but are only appropriate for deep bass (sub 40Hz) augmentation. REL subwoofers are a good embodiment of this line of thought.
As far as amps go, some amps have slightly different deep bass qualities, but these differences are not comparable to the influence of room acoustics.
As far as amps go, some amps have slightly different deep bass qualities, but these differences are not comparable to the influence of room acoustics.