how I installed my eagle mach sound card.
photo 1 ;
channel 6 track motor use a y connector and put track motor cable and the orange lead to sound card.
photo 2;
channel 7 4th valve .put signal reversing connector into channel 7, put white lead for sound card into one of the output leads and 4th valve into the other.
at the front of the excavator there is a strip connector to supply the esc,s . I connected the power cables for the sound card into one these.
mine didn't work how I wanted ( when stick moved the revs decreased) on the signal reversing lead there is a small pot ( photo 3) adjust left or right to change out put signal, once done the revs will increase with stick movement.
I don't know ( haven't tried) if it matters which lead you use that comes out of signal reverser . but I do know if the signal is reversed to the 4th valve when you try to start the pump it will stall( not good swap wires around or try adjusting the pot 180 degrees)
a bit of guess work and it works perfect.
last picture job done.
hope this helps.
cheers andy