The B&K St 140 isn't that comfortable driving sub 8 Ohm loads.
The Thiel CS 2's with their smooth, steady 6 Ohm nominal / 5 Ohm minimum rated impedance is one of the very few Thiel's suited to the B&K St 140. A nice sonic match and terrific combined value.
https://www.stereophile.com/content/bk-st-140-power-amplifier-1989-measurements
https://www.stereophile.com/content/thiel-cs2-loudspeaker-measurements