[mcmlxix]

I think the Audi R8 has dual calipers in the rear, one may be an emergency brake.

I would think that the master cylinder would need the appropriate size for all the pistons in both calipers, like you said, no different than one huge 6 piston caliper. I think you might need to split the brake line and feed both calipers rather than in series.

This would be great for someone who wants to run smaller wheels and can't fit the big 6 piston calipers...