Yamaha DTXpress/DTXplorer/DTXtreme

Hello everyone,
  I recently played a DTXpress II electronic drumset for 2 days.  I 
loved playing it live and was amazed with the quality and 
sensitivity...especially the snare!  However, when I used the 2 
lineouts to input into my 4-track cassette recorder, I noticed the 
outputs were putting out a slightly distorted signal! This was not 
noticeable when the headphone jack was used!  This was also confirmed 
by someone else on some online forums.  Can someone please tell me 
how to fix this distortion because it sounds terrible and is 
annoying?  I also noticed moderate unintended distortion on the drums 
in this heavy metal recording in the "files section.  I need a 
drumset very soon too!  Thanks in advance.

best regards,
Altay