The 50S and the 5S already come with the HD speakers included so the SC-A0325 is compatible with the 50S and the SC-A0326 is compatible with the 5S.
Here are which Sena headsets are compatible with the HD speakers:
SC-A0325 - HD Speakers Type A
- 20S EVO
SC-A0326 - HD Speakers Type B
- 10C EVO
- 10C Pro
Note: To use the HD speakers on a compatible headset, the firmware version that includes HD Speaker Support needs to be installed on the headset.