It's not the audio circuit per se - the CE-RH1 remote requires a voltage to be present on the "key" pin in the socket, which for the C860 happens to be the sleeve (ground is first ring, which is backwards IMHO and was reversed in the Cxx00's).
A headphone jack will touch the tip and each ring against the live "key" while it's being inserted; this is what causes the crackling you hear.
It's still live when the Z is suspended so it is possible to unsuspend it using the remote; although I'm not sure pdaXrom is configured to take advantage of it.