I found the WA8LMF universal sound card audio attenuator works pretty good and created a few PCB’s for it.
Version 2 – I found on a few of my radios the attenuation was a little too much. So I created a second version replacing the 10K resistors with trimmers. This version also includes stereo jacks so pre-assembled cables can be used. A Sacagawea dollar coin tube makes a nice little case for it! V2 kits are now available in the store. Instructions and manual can be found here.