The best implementation is the Meridians, which use a proprietary interface. If the digitial interface to the speakers were standardized, seperate amps would eventually go the way of the dinosaur. Because then all the choices the audiophile craves would be available by merely replacing the speakers. Marketing and sales are to blame not technology.
I do not own Meridian speakers. Some days I wish I had bought the DSP8000's and not my huge mono block amps/speakers. John's post above summarizes things pretty well, but he dismisses the digital transport layer, which I feel is critical.
The digital transfer of data, allows the crossovers to be implemented in DSP's, and it allows a seperate DAC for each driver type. The direct coupling of the amps to each driver has everything over convential amps (single amp, bi amp, tri amp whatever). When an amp is tailored to a specific driver, and a specific wire interface, many assumptions can be made and held, that greatly improve the control of the cone.
If you have any doubts, I repeat what John asks, read Mr. Stewarts technical articles. But first, seek out a Meridian dealer, and sit infront of a 861/800/DSP8000 system, and get blown away. Go ahead, add up the cost (you only need an 861 just to listen to CD's). Yeah, eah piece is expensive, but no amps, no cables. The total system price is less than a comparable stand system.
It is rumoured that several other consumer scale mfg's are working on speaker system very similiar in concept to the DSP8000. It is hoped that HDMI or whatever digital interface that gets standardized will open the way for this.