I've had my Vandy 5A Carbons for about 18 months now; they replaced my beloved Maggie IIs which were coupled with an ancient Vandy 2W powered subwoof. Given the right source material, the 5s just seem to disappear from the room, leaving only the music. Setting up the high-pass filters to match your amp's input impedance is a matter of setting a few DIP switches and takes about a minute to figure out and do. You can spend as much or as little time as you wish emplacing and angling the speaks for a single sweet spot to take advantage of Richard's efforts to provide perfect imaging, or just muscle the things around till they sound right in your room. Mine are toed-outward about 30 degrees and about 18-inches from the long wall they're on, and from my off-center listening chair the imaging is perfect - and nearly as perfect at the other end of a 7-foot couch.
As for power, I run a pair of Vacuum Tube Audio M-125 monoblocks (each with four KT-88- 6550-type tubes in push-pull configuration) and Roy Mottram tube preamps. In triode mode the monoblocks step down to about 65 watts per side and I am able to rattle the dishes three houses down the street with cannon-fire on 1812 Overture; however the true joy is hearing the difference between the "tink" of a cymbal most speakers give you to the "ding" the Vandies deliver.
Agreed with all above posters, it's GIGO. Feed the Vandersteen 5A Carbons fresh lobster and they'll serve you fresh lobster. Feed 'em canned tuna and that's what'll come out. They neither add nor subtract anything from your playback media. Therein their beauty.
Not mentioned by others here, but IMO vital, is that these wonderful speakers be discreetly bi-wired as the manual recommends. I was bi-wiring through a single four-conductor Canares cable and was quite content. One bored afternoon I doubled-up with some extra cable, nothing fancy, for true bi-wiring and "WHOMP!!" the backside of the soundstage just fell away. An unbelievable improvement over what I already thought was perfection. Don't ask my why; it makes no sense electrically. (I've since upgraded the speaker cabling and connections a bit, none of that $1,000 a foot crap, but nothing made the improvement of the magnitude that discrete bi-wiring does, even if you have to use lamp cord.)
One caution if you're going to spend Lamborghini money on custom cables: Be sure the speaker ends are spades that will fit the rather smallish connectors on the back of the speaks. For DIY cables, Audioquest makes a silver spade that fits just right for 10-12 gauge wire; otherwise you'll likely spend a few hours on a grinding wheel.
Bottom line is: the 5A Carbons have eliminated one baffling and very expensive variable in the hi-fi equation. They are, to my ear, invisible.