This is my guess:
The two RCA "input" connect to a preamp L and R output.
The RCA jacks marked "amp" output low-pass signal (32, 100 or 200Hz) to two external power amp channels to drive L and R woofer.
The two external power amp channels outputs connect to "right amp" and "left amp" spring connectors via speaker cables.
The left and right tweeter will powered by the internal amp.
The two RCA "input" connect to a preamp L and R output.
The RCA jacks marked "amp" output low-pass signal (32, 100 or 200Hz) to two external power amp channels to drive L and R woofer.
The two external power amp channels outputs connect to "right amp" and "left amp" spring connectors via speaker cables.
The left and right tweeter will powered by the internal amp.
Wonder what do the 4 "calibrate" buttons and knobs do?I guess it is to set the gain of internal power amp to match the external "woofer" amps.