Sound Check on iPod

Is it me, or does the iPod Classic not respond if playing audio via its data socket and has 'Sound Check' engaged..?

iTunes will alter playing volume if 'Sound Check' is selected, so it is possible for this to be done via a data-stream (rather than pure analogue audio), but when I select it on my iPod, the volume over the data connection does not get altered / evened out.

Is there a fault on my iPod..?
I'm getting a bit tired of constantly having to reach for the volume knob on the radio in my truck, due to vastly different volume levels on different tracks.

Any ideas would be much apreciated.
Thanks - Dave