Yamaha DTXpress/DTXplorer/DTXtreme

I've been tearing my hair out for two weeks over a problem and I'm 
hoping that some of you DTXpress experts can give me a hand.  
Someone donated a DTXpress drum kit to my church, which I am now 
expected to play.  Trouble is, I don't have a manual.  I've figured 
out most of the necessary stuff, but I'm having trouble choosing the 
bass drum sound that I want.  Since this is Church, I don't want it 
to be too overpowering.  The trouble is that most (but not all) of 
the preset drum kits seem to have two distinct sounds generated when 
I hit the bass pedal.  One is the sound that I picked through 
the "voice" control, and I can control the volume of that sound.  If 
I press the "voice" button repeatedly, that is the sound I hear.  
The second sound is added when I use the bass pedal, and I can't 
find where it is programmed or how to turn it down!  The "Pad 9 
controlling 10" option is turned off, so it is not coming from 
there.  Has anyone else experienced this?  Please help!

Many thanks, Mike