According to eesdr.com/images/Document/SunSDR2_DX/SunSDR2DX-ACOM.pdf, for keying the PA I need cable which will connect EXTCTRL of SunSDR and Acom KEY IN in the following way:
X8/pin13 to the RCA center pin,
GND/pin15 to the RCA shield,
and I have to turn PA to on in EESDR software.

Do I need anything else, any e.g. diode, or relay in between TRX and PA?

MNI TNX,

73, Vedo.