I would like to adress what Trelja commented on, in that I understand an "audiophile's" desire to "tinker" and find combo's he feels best match his speakers/needs. Really however, whether an amp is built into a speaker or not makes no difference from one scenario to the next. If that amp is maximized to sound it's best, and perform to highest standards, it's a much better proposition than doing "passive amplification/crossover" approach BY A LOT!
i WOULD TAKE ANY DAY A BETTER ACTIVE DESIGN with built in amp over my best amp sellection on my favorit speakers, yes!..that is if I like the overall sound of the active speaker to begin with. If a speaker has the ultra refined transparancy I've come to appreaciate from companies like Thiels, Wilson's, Magnapan's, Merlin VSM'setc), and has kept that integrity in an active design(only better in dynamics and soundstage/realism), then I'm all for it! If a company can make a successful effort with the above mentioned speaker designs, I wholehartedly feel they can keep "that sound" with careful amp sellection in an active effort, yes!!!...why not?
If that's the case, I wouldn't sweat the "amp selection" any. I'll gladely take the "active advantage", yes sir!..much more control, dynamics, pressence, realism, power, finnesse, speed, wow, you name it! (if you want a tast in a "quasi active design", go hear Avantgardes).
Although, you don't have to have "built in amp's" to have an "active speaker design". Avlar out of Systems Design Group in Redondo Beach, California makes a very high end sounding "active speaker" ($12k-30k/pr I think), that is basically a "speaker enclosure with drives(although well designed ones)" minus crossover. You use an external crossover(they used Krell at one point), with their own amplification(was Krell). In this case, you could use whatever amp's and crossover you chose!...YOU DON'T HAVE TO BE STUCK WITH THIS COMBO! you could use any amp/crossover you chose...this might be a better OPTION for those who want to tinker..and those speakers sound exceptional! I'd take those over any typical passive high end design, if willing to spend the money, indeed...very very dynamic/powerful(stomps passive designs in the dirt!), yet very refined and high end sound. The best I've heard in an active design personally.
Speaker makers can offer a choice of "built in amp/crossover" or "external amp/crossover" and still maintain an "all active design"! The latter let's you chose your weapons, the former just offers a simpler, yet effective approach, like I presume ATC offers.
I've not yet heard ATC's, only heard reviews on the $90K one's.
Anyway, It would be "nothing" for a company to build active speakers, and offer an outboard external active crossover that works extremely well, then let you either chose your amp's (like we already do all the time anyway), or chose theirs! Simple really. Yet, every high end speaker maker has given me all the excuses why they are "not interested" enlarge in active speakers. Mainly, "heat"(although digital amps run cool), space(BS if you ask me), cost(what cost?!!) marketing problems(I guess they think everyone is stuck in a "passsive speaker rut" in the home market..dunno.), etc.
I've said it before and I'll say it again..."high end speakers are stuck in the passive realm with limited dynamic transparancy and realism" If you think not, just pop in any heavy rock, techno, rap, ESPECAILLY FULL RANGE MOVIE TRACKS FROM dd/dts, and listen to your pathetic full range speakers distort, flatten out, and cry for dynamic help!!!! Basically, most all high end passives sound pathetically whimpy and laid back dynamically for the most part. When you feed em the goods, they go "bye bye"! (ok for Dianna Krall and "pawn shop", but not for Metalica sorry).
MORE ACTIVE SPEAKERS!!!!!!!!!!!!!!!!!!!!!!!!! (I'd promote Avantgarde's if you din't have to sit right between the freakin things....)