from a quick google search which led to a find on ebay... this is what it states.
SLB-R4 (4 channel) to receive the balanced signal and convert it so your standard amp can have the advantages of the SymbiLink System.
The SLB-R4 allows the system to drive two amplifiers from a single receiver and still maintain any fading functions.
4-Channel Balanced Line Receiver
· Allows any system to recognize SymbiLink™ Balanced technology.
· Creates a closed, balanced system using a SymbiLink™ Balanced transmitter
· Quality ZAPCO construction
** Designed and Manufactured in the USA **
Basically allows an amp to learn some kind of newer technology?