In general, I think you have a hard time beating a QSC PLX series power amp. For the overall combination of power tone and weight, they are hard to beat. When weight is no object, many people swear by the Crest CA-9. I use a PLX and I am so happy with the power section that I can't comprehend how the Crest could be noticeably better, though I haven't ever had them side by side at gig volumes. If you really want the low B to work, there's no such thing as too much power.
The preamp selection is a matter of personal taste and features. The Alembic preamps have great tone, but not much in the way of features. More modern designs give you additional EQ features, foot-switchable loops and additional channels, or digital effects.
Your choice has to depend on what sort of music you're looking to play. For a cover band that's trying to duplicate the originals as closely as possible, I think the latest Line6 Live series gear is great. The tones aren't the same as actually carrying half a dozen amps with you, but it's close enough for that sort of work. If you're doing your own thing, then you really just need to listen to some different things and see what speaks to you.
Speakers will be critical to getting what you want out of that low B string. It's hard to get the most out of a B string with really portable gear and I gave up on doing it. Dave's rig is great, but how does it match up with what you're trying to do in terms of space occupation and portability? I know I wouldn't want to lug that around on a regular basis. I am a big fan of the tone of the Schroeder cabinets and use a 21012L for any size room or outdoors. They have a great punch to allow you to really hear yourself on stage in spite of what the guitars may be doing. See if there's a dealer in your area and go out to give them a listen.
I think a PLX power amp is an easy decision. Beyond that, there may be some trial and error to get what sounds best to you.
