Yamaha DTXpress/DTXplorer/DTXtreme

Hi everyone, this is my first post and as I'm new to the forum 
apologies if this has been posted before.

Recently bought a DTXpress III special and I'm pretty impressed apart 
from one thing - the drum parts on the built in songs are far too
loud 
compared to the sounds I generate when hitting the pads.

I can't work out how to adjust the volume of the drum part of the
song 
independently. The manual isn't much help as it only explains how to 
mute the drum part but that is not what I want to do - I only want to 
reduce the volume.

If I adjust the main volume to make the drum parts of the built in 
songs at an acceptable level then I can't hear what I am playing.

Anyone else having this problem. Any help would be greatly
appreciated.

By the way - great forum, loads of good info here.