Yamaha DTXpress/DTXplorer/DTXtreme

I have not tried it, but as far as I know, the Roland pads should work.

Did you try the editing the trigger settings to select a different pad
type (shift+trigger)?  Also, by pressing the voice button you should
be able to see which pad has been detected when you hit it, e.g. snare
or snrR1 for the rim.  You also need to make sure there is a voice set
up for the rim.

You don't say where you are, but in the USA you could buy the parts
you need (e.g. Yamaha pads) from Drumbalaya http://www.drumbalaya.com/
or in Europe from Thomman http://www.thomann.de/

You did well to last two years with a DD55 - I lasted a month before I
was looking at the DTXpress.

Keith.