Yamaha DTXpress/DTXplorer/DTXtreme

Looks like I joined just in time.... I checked my bass and found it 
was wearing thin.  The tip to put a bass pad came in handy.  It 
seems to have dropped the already hurting volume though so I had to 
go thru the rest of my triggers and drop them a few notches to 
compensate. The bass volume is maxed out. New questions: What 
happens when the internal battery dies? And Can I daisey chain 
brains by plugging the out of one into tha aux in of another?  Can I 
use a DTXpress with my DTXpress II?