Well, Sticking to one brand is nice looking and all, but the problem is that no one company makes the best gear.
For a perfect example. Alpine makes a fine head unit. There is better for same or less, but theirs is okay. Alpine makes crappy interior speakers for the price. For the same price you can get better from eclipse, mb quart, kicker, focal, morel, morelusa, etc etc.
alpine amps are fine, for the same price you can get double the wattage and just as clean sound from manufacturers like planet audio, kicker, rockford (i hate rockford, but they get the job done) phoenix gold, lightning audio staggered amplifiers, etc
subs, the X's are fine, the R's are fair, the S's suck a$$ like no tomorrow. If you are not going to spend the money on the X's, then I would go with other brands, etc.
Most people like their amps to be the same brand because it matches, that's something that I agree with, but for all the gear in the car?? no, I would disagree.
good luck