I currently use older Emotivas - UPA2 and UPA7. They are pretty good amps.
As to the XPA, I think you may have to ship the amp back to Emotiva for the modular XPAs to add modules (and may have to pay). The new XPA (Gen 3) have switching power supplies...from the Emotiva forum, it seems mixed opinions on these versus the older XPA with torroidal transformers.