I'd be very surprised if the item was bridgable and not get a mention in the spec sheet I posted earlier. Have you gone back to your dealer and asked him to clarify? Can he not point out how it's done?
There is no sign of any such switch on the rear of the unit though there may be dip switches inside the unit. Theres no reference whatsoever this facility on the Plinius website either - and they do mention other units having this (the SA-103 for example). Sounds like a rather unfortunate misunderstanding if you now have two P10's and can't bi-amp.