Rockport speakers have outstanding transient response. There is a pair of Rockport Technologies Cygnus for sale on Audiogon - this is a $65k speaker on sale for $36.5k.
i have the Atria IIs, two levels down from the Cygnus, they are totally transparent and have an ability to retain resolution over an amazing dynamic range. They will happily play at any level your hearing could stand and at the end of a piano piece you can hear when the dampers touch the strings.
If you Google - Rockport speakers transients - you will get a good description of the sound.
The Cygnus and Atria models use the same mids and tweeters, the Cygnus has beefier woofers.
As you move up the range the cabinets become even more advanced.