Tough predicament you are in.
I will say, however, that the "for off road use only" mark on the Ti can is written in a very obscure place, not facing the casual (or even suspicious) observer, and you (or the person looking for it) will only find it if you know exactly where to look. Otherwise, these cans have the factory stamp on the outside, so I can't imagine anyone would think of these things as being aftermarket (illegal) accessories. I would also be shocked if there is much of a db change with these pipes over stock, especially anywhere under 4,000 RPM.
good luck!