Harman/Kardon Citation twenty-one
Harman/Kardon Citation twenty-two
Harman/Kardon Citation twenty-three
Harman/Kardon Citation twenty-four

Components developped by Richard Miller, Marty Zanfino and Mr Zekiya.
These ultimate Citation either sonically failed to convince or weren't advertised much due to a dwindling high-end market... Apparently very rare units at any rate.

The usual Harman/Kardon trickery was however at work : wide bandwidth, high slew rates and rise times, impressive output current capacity (HCC). But this was somewhat down a few notches in build quality and the "absolute" Citation units were those from the previous decade: Citation XX & Citation XXP , Citation X-1 and Citation X-II - when High-Fidelity was riding high. And the dark-ish looks were perhaps a little too... dark, too.
After this low-profile set of high-end units, and besides buying half the brands on planet Earth, H/K went home-theater full-size, low and high.

The Twenty One is the preamplifier, the Twenty Two and Twenty Four the amplifiers, the Twenty Three is the "Active Tracking" tuner.
You may find reviews for Twenty Two here, for the Twenty Three here and for the Twenty Four here.