In my long tandem career, I don't recall ever knowing of anyone that used tubulars on their big bike. Heard of them being used in velodrome, but not on the road. Might be an interesting experiment if you could find tubular rims that could stand up to tandem (ab)use. Not sure that the tires wouldn't detach and roll off under hard cornering given the weight of a tandem. If you try it, just don't use your face as a brakepad

Nice looking Cannondale by the way. How long have you been riding it? Is your daughter the numero uno stoker?

Rick