I did not want to jump in on this right away since my opinion is biased being a Hawg-Wired Dealer. Since no one else has answered i will give you my opinion.
For the Pre-06 bikes sound wise you can do much better than the stock speakers that come in the bikes from the factory. (The stock Harmon Kardon speakers in the 06 and later bikes are greatly improved) Pioneer, Alpine, Hog-Tunes, Hawg-Wired etc, etc...are all better than the stockers. The big difference that sets the hawg-wired speakers apart is that the are sealed. If you look at most aftermarket speakers the voice coil is exposed. Any amount of moisture or dust and debris that gets into the voice coil will eventually destroy it.
The magnet size can be deceiving as well. For Example the new speakers from Harmon Kardon use a neodymium (sp) magnet that ounce for ounce if much much stronger than a standard magnet.
The color codes for your speakers are:
Left + White / Orange
Left - Light Green / White
Right + Gray / Red
Right - Light Green / Black
For Power to your XM you can use the Orange wire on the back of you cigarette lighter....