does a subwoofer kill stereo sound?

There is no need to spend lots of money on a "state of the art" amp to drive a "state of the art" sub.

Disagree. Most subs (I mean 99%) simply distort so badly that they ruin the sound (at least at usable SPL's in the ultra LF range of 20 to 30 Hz).

It is EXTREMELY difficult to produce low frequencies at reasonable SPL without distortion and therefore extremely expensive to do it right (to audiophile standards).

The same can be said for speakers - it is just plain difficult to do ultra-LF well - the manufacturer may claim performance to 20 HZ on a full range speaker but what they don't tell you is that you will be hearing upwards of 10% THD at anything nearing useful SPL levels.

Distinct bass lines from drums is something that can be heard on a good system as the timbre is quite different (even if they may overlap in frequency range). The trick is to have a critically damped design as opposed to a ported resonant design. (although resonance gains efficiency and SPL it has a down side in that it destroys timbre and will make differences between bass and drums that much harder to hear)

Here is a little more why I believe resonance and THD is important in ultra LF.

Resonance is important because of "masking". Masking is what is used to create lossy MPEG files that sound almost identical to lossless files. Masking is the well known fact that loud low frequency sounds will mask higher frequency sounds to the human ear/brain system. Therefore, if you cannot hear these higher frequencies (due to LF sounds) then this detail can simply be removed from the audio files (reducing the file size dramatically), whenever there is "masking" going on. All you need is a clever algorithm to recognize when masking will occur and you can compress any file.

THD is especially important in ultra LF because your hearing sensitivity increases dramatically from 20 Hz to 100 HZ. Typically you are some 40 db more sensitive in hearing at 100 Hz compared to 20 HZ. This means that even minuscule levels of distortion in the ultra LF (20 to 30 Hz) can still amount to highly audible harmonic distortion effects at 100 Hz and above (altering dramatically the timbre of the sound). Since the distortion is harmonic it generally does not sound bad (and will not change the fundamental note) but most subs, which distort badly, will make everything sound extremely bass heavy (making it much harder to hear details) Of course, since it doesn't sound bad most people think these subwoofers are amazingly "impressive" - as they hear such heavy handed bass (deep bass they think). Actually a good precision subwoofer should not sound "impressive" at all!