You really want to overcome your issues with quality, not quantity. That really strikes me as the main issue from what I saw in your first post. More power does not make better sound. If you multiply suck, times five, it means five suck, not one good.
So, I'm not a speaker expert, but you do want to get some decent newer generation speakers.
It's pretty easy to spend $1,000+ on decent speakers, so you will have to determine a budget, and keep your expectations in line with your budget. IMO a good subwoofer typically costs over $500 alone for the most basic requirements of quality in a pre-finished product. Nothing but that one speaker.
Your room, like the speakers, plays a huge part in the quality of the audio playback, and if you have any speakers in a bright room, then those highs will be accentuated due to the hard surfaces, and may create a very 'shrill' environment.