OK, here's my post-install report -
The BassLink is near perfect for my use. Wow, what an upgrade in the bass!! I'm not going to compete in any car stereo contests, but produces lots of bass from the stock system! I especially like its tune-ability and the fact it hooks up to the speaker leads, with no need for remote 12V turn-on wire.
I tried installing the component speakers, but was confounded by the factory built-in cross-over. The best way to get the most out of component speakers is to use the crossover that they come with. The factory woofer is actually very nice, with a nice rubber surround. I heard no improvement (and maybe some extra buzzes and rattles) when I installed Infinity's woofer.
The tweeters were a spectacular improvement over the stock tweeters, even hooked up to the stock wiring/crossover (and I see no easy way around that). MUCH brighter and more efficient! So my plan is to box up and return the component Infinity speakers and return them to Crutchfield (they are excellent about that) and instead buy just the tweeters (Model #1011T). In fact, I found a set of 1011T's on Crutchfield's scratch-n-dent and so I've already ordered them; it's just a matter of returning the component system.
Summary: The BassLink is an excellent solution for adding bass to a stock system, and the 1011T's are all you need to boost the high end. I can't wait for those tweeters to arrive!!
PS - I was VERY impressed by BMW's attention to detail, evident when I removed the door panel. TREMENDOUS attention to sealing and detail! Molded plastic instead of sheet plastic, molded foam gaskets instead of a chintzy caulk line. Robust fasteners. I could go on, but my overall impression was that the E39's door designers/engineers didn't get any memo about saving cost or weight...