I'm sorry to butt in when I have no real experience with Linn gear other than having heard a friend's system both passive and Aktiv (using no special rack, by the way), but while I have heard sonic differences from vibration control devices and racks I have never heard a sonic difference from them as significant or pronounced as the one you describe. I'm curious, do you biamp from the same rack with no ill effects? If so, that should rule out the room, the rack and the speakers; I'd think something has to be wrong in the amps--maybe they set them up with crossover configurations for a different Linn (you are using Linn speakers, I assume) speaker by mistake?