Not sure what "bolt on hooks" are but here is a post showing how NCX's X-pipe has the supports welded onto it so the system has some support:

http://www.xoutpost.com/x5-e53-forum/...haust-mod.html

I haven't been under my X in a while but I do not think the angle of the pipe going into the X-pipe is much of an issue. There should be enough pipe left after the resonator is removed to weld on the X-pipe.

I think the other guys who have had it done have had the supports welded on and the price was around $100 - $150.

To answer Bob's question the X-pipe is a bit quieter then the striaght pipes.