are all amps equal

"Also, I would recommend buying a subwoofer since you're not planning to
replace the BE-718, which only go to 42Hz, and therefore are missing a
significant range of bass where much of the music lies."

Lowest bass or electric bass string is 41.2Hz (I think). Piano goes down to 27Hz (A) but is seldom used. Unless somebody listens to symphonic orchestra with big drums going down very low or needs special effects for the home theater than 42Hz should be fine (if its really 42Hz).

I'm perhaps missing something but there were known bass strings reaching 17.5Hz. I don't see (hear) any sense since it's not audible. Tvad - can you comment?

Keslerd - good choice - 352 or 402 should do it.

Re the question about subs, although it is true that there won't be much to listen to below 40Hz or so, a good sub can be expected to handle the range from say 40 to 80Hz more cleanly (with less distortion) than the Usher's 7 inch mid/low frequency driver. Especially at high volume levels.

Regards,
-- Al

Tvad - I understand, but shouldn't 42 Hz be fine if somebody listens to jazz or popular music (and not the organs or double bassoon).