up for your consideration is a NEW OLDER STOCK David Clark Headset adapter for various KENWOOD PORTABLE RADIOS.
i've tested it with my KENWOOD NX5300 and it will key the radio just fine, but i don't have a headset to fully test. I'm sure it works fine. 

this would be great for your Kenwood radio when you are in high noise environments with a compatible david clark headset, not included

google says it works on the following radios

The Kenwood NX-5300 uses a multi-pin Hirose connector, meaning speaker mics designed for this radio are compatible with other Kenwood portables using the same interface.
Official compatible mics for these models include the KMC-25, KMC-41, KMC-42W, and KMC-72W so if your radio works with one of these mics, it should work with this. 

kenwood radio and headset not included