My personal opinion, you are reading way too much into the specs. Speaker power ratings are virtually useless.
Cabinets are VERY much part of the speaker and most definitely affect the sound.
In short answer to your 'below 50Hz' question, buy a subwoofer. That is what it was designed for. Some towers have incorporated larger bass drivers (and 12" IS rather large for a typical home sub let alone a tower) to use for bass frequencies, but i have yet to hear one that sounds any good.
If you want more info on wattages, power use, speaker specs, etc. do some serious searching through these forums. You will find plenty of info on all those topics.
