v1.1 was to expand the volume range for the wireless headphones.
v1.2 was to put in the necessary software for the change in our memory chips (nothing other than a different manufacturer)
v1.3 is the current version and is to address what some call the "mono to stereo problem". It's not really going from mono to stereo - it's all stereo, the phase of the audio signals change. I addressed this in an earlier thread. It also will work with mono headphones (wired) now. With the phase rotation of the 2 channels, mono headphones were going quiet when that happened. This detector is recommended to use stereo, but now mono phones can be used.
To get the full advantage of the audio fixes, yes the detector and headphones need to be sent in. All processors need to be reprogrammed. The detector and the headphones do not need to have the same software version - they will work with separate versions. So if you only send in the headphones, your range of audio on the wireless headphones will not be increased, but you will get the "mono to stereo" fix for the headphones (but not for the wired phones).