The Pioneer 6900 Pro's speakers you mentioned have good bass but the tweets can be harsh, especially with 4 of them. DD VO 6x9's would be a much warmer sounding speaker, but may need a horn to get some good highs. If you are going for more bass you would be better off with an 8" or 10" in the bags, You could even run 2 8's in the bags with the proper mount. The Alpine amp you mentioned is a bit pricey for the size and power. There are several amps that will get you as much or more power and will have a clean sound for less money. There are some 6 channel amps that will run your setup. If you are gonig for loud and clear audio I would look into a pro audio setup, like PRV, MMats, Beyma or DD Audio. You'll prob spend a lot less for a lot more sound.
2007 SB Stage 1, PCV, 30/70 swap, fabbed fenders, w/ quick release bags fairing and tour pack, lots of powder, flake and marbled paint.
2008 Road Glide - Stage 1, added lowers and Tour Pak, and upgraded audio.