I am sure you can use an RCA Y adapter to apply a GC RCA unit. Make it the shortest adapter you can find, one with the least metal and dielectric possible.
For that matter you could also use a Y adapter for the headphones, with a tip and ring male plug attached to a female RCA and plugged into one of the Y's. I have no idea how this would sound, but no harm can come from trying it out. You may need two RCA GC's to make this work, unless the particular headphone has a common ground / return wire, rather than separate ones for each channel.
A tip and ring plug comes in a variety of sizes, 1/4" mono, stereo and balanced stereo, with similar types available for mini-plugs. These are just the official name for the plugs usually found on the end of your headphone cables.
For that matter you could also use a Y adapter for the headphones, with a tip and ring male plug attached to a female RCA and plugged into one of the Y's. I have no idea how this would sound, but no harm can come from trying it out. You may need two RCA GC's to make this work, unless the particular headphone has a common ground / return wire, rather than separate ones for each channel.
A tip and ring plug comes in a variety of sizes, 1/4" mono, stereo and balanced stereo, with similar types available for mini-plugs. These are just the official name for the plugs usually found on the end of your headphone cables.