Pete,
The DTXpress doesn't come with speakers. The ones you have seen in
brochures will probably be the Yamaha ones, but they don't seem to be
very highly rated by people who have heard them (and they are
expensive). In general a keyboard speaker with built in amplifier is
considered to be a good option. I use a bi-amped PA speaker with 15"
bass/200W and horn tweeter with 100W.
Keith.