Sussed it - the secret seems to be not to run the WASAPI Output plug-in in "Exclusive Mode" - then the MM volume control kicks in.

Thanks for the reply - the volume control doesn't seem to have any effect with Directsound either.

This is likely because you are using Wasapi, volume controls are disabled by design when using Wasapi or ASIO. Because this way the audio remains bit perfect (read windows mixer doesn't get to tamper and degrade the sound quality). iTunes doesn't support bit perfect audio and WMP probably doesn't either (not with default settings anyway).

If you want to disable Wasapi just to enable volume control, then change the Options > output plugin to DirectSound. If it is however already set on directsound then I have no idea what is causing it

When playing through a USB connected Musical Fidelity V-DAC, I'm getting an issue where the volume control from within MM4 player [1459] doesn't have any effect on the volume. This DAC is shown up as a generic "USB Audio DAC" in device manager and volume can't be controlled whatever output plug-in is used. When I use WMP or iTunes, the player volume controls work fine.

Let me know if you'd like a debug log etc.

Thanks
John