Yamaha DTXpress/DTXplorer/DTXtreme

Hi! 
 
I would like to record my performance with the preset songs, with 
the sequencer. In the "song" menu, there is an option to copy 
any preset song into a user-song slot. So I do this, but when I 
want to record my playing, I can't mute the drum part of the song 
(I mean, when I playback the song, I hear MY part and the 
pre-recorded part). 
 
I want to delete the drum part of the song. I have tried to mute 
channel 10, but then, I can't hear my playing!!! 
 
My DTXPress is a first-model. Is there any way to record my 
playing with a preset song? 
 
I know, this must be a very novice question. I feel ashamed, but 
I'm getting crazy with this.