I have tried talking to the server using shell echo and cat commands in different terminal windows.
Lyx just seems to parrot the commands e.g. echo "LYXCMD:sampleclient:hello" >.lyxpipe.in gets INFO:sampleclient:hello: (from cat .lyxpipe.out) and echo "LYXCMD:sampleclient:get-xy:" >.lyxpipe.in gets INFO:sampleclient:get-xy: Is there some Lyx setup command or build option I have missed?