I follow you. I haven't seen a suitable bike that will gain much over the samba for the price; the cannondale would need disc brakes, the suspension fork, rear suspension post, shipping/travel cost, and maybe more dependent on condition. I read about issues with their rigid forks with disc brakes on some models too. I picked up the samba for less than $500 and figure to spend $500-$1100 for a total investment of $1000-$1600, completely decked out. I can't find anything close to that with similar components, which I figure are aftermarket parts that could be transferred to a dedicated mtb tandem frame in the future.
Thanks for the ideas, I'd not heard of the 'brake therapy'- I'll check it out. I've called about the arai and no one had it. If anyone knows of someone, please speak up.