I hope I am wrong, but it appears that, unlike the 770, there is no live control for volume. It has the VH instead.
Bernie I just had some time to test this on my S970 and it works perfectly...
YES you can assign the LIVE KNOBS to control the AUX Volume of a LT, Phone, Mp3 Player, etc, as shown here, ...open your live knob menu scroll down to AUX Volume & push assign,...that's it.
A great feature.
enjoy