Yamaha DTXpress/DTXplorer/DTXtreme

Hi,

I am considering purchasing a Yamaha DTXPress module.  My sole 
purpose for buying this module is to use it as a trigger system for 
my acoustic set.  Is this possible?  I read one review that stated 
that conventional drum triggers (like ddrum, or roland) could not be 
used with this module?  Is this true?  If so, how many triggers can 
be hooked up to it?

Thanks a lot!