I got it working using your method. On H9-2, RCV CH has to be set to 2 (for H9-2)

XMT CH has to be set to 3 (for H9-3)

RCV.CTL has to be set to NXT.CC#A, LST.CC#B

XMT CC for RING and T+R have to be set to the CC#s on H9-1.

CTL.XMT set to ON,

PGM.XMT has to be turned ON.

OUTPUT has to be set to MERGE.

H9-3 has to be set to:

RCV CH: 3

RV.CTL: NXT.CC#A & LST.CC#B