Hi mate, most of my experience is around SME's so can't offer much re using foreign entities in the way you are suggesting, other than that there are not meant to be any common loopholes. Trying to use the double taxation agreements is obviously extreme as you note and I can't say I've ever come across anyone trying to take advantage of them in that way... You're certainly making me curious as to how much profit you're turning over to be even looking into these areas as possible tax minimisation strategies. Be careful how elaborate you get... It's never worth the consequences of being done for tax avoidance and if you've got some big dollars behind you, then they may just come poking around.
And yes, you're correct, if you're earning serious money, then you're going to pay serious tax. Accountants can really only set you up to minimise tax, although that is usually enough to make a big difference for most people.
If something in the tax world seems too good to be true, then it usually is.
