... with your permission
Excuse my verbosity -- often necessary to explain techie things to my former, non-engineering superiors.
Correct about a probationary member.
There is nothing wrong with the cable harness. You need to absorb more earphone power before going into the camera.
I am sure you can easily obtain the parts. For example, In the States there is Radio Shack who sells the parts to build the pads (that is what they are called). Then there are purveryors to musicians like Guitar Center and Sam Ash Music, who sell pre-built adapters to help musicians plug various types of audio gear together.
Again let me suggest you make friends with a technician in an avionics shoppe. He, most likely has the parts to build the pad in his tool box. Protocol in the States is a 6-pack of beer. With parts in hand, it should take maybe 15 minutes to build. I suggest a 15 or 20 dB pad. Anyone with a modicum of knowledge will know what that means! You can also find a local Amateur Radio operator who is usually suceptible to the same payment protocol or even a tour of the flight deck. Maybe that is the best idea because he can test and make adjustments on-site.
E-mail directly if you have questions.
robert AT sudock.com
Cheers!