(Some research on the interface between the transceiver and amplifier)
The idea is simple. My main base station line consists of two Yaesu radios - FT-2000D and newer FT-991. With two inputs of Yaesu QUADRA VL-1000 amplifier can electronically switch and operate alternatively one of them. Unfortunately main base station speaker Yaesu SP2000* connected with two high quality screening cables to two transceivers as above can not be switched electronically due to the lack of an electronic switch integrated with VL-1000 or station system. There is no such signal line.
*Can be mentioned that SP2000 main station speaker is separately grounded with additional grounding clamp (My SP2000 modification is described in separate article with FT-2000D portal menu tab). This is my additional modification of the SP2000 speaker. Personally, I hate all kinds of plastic cases at the station and ungrounded devices.