Let it be Frank. Don't get all that concerned about the ATA. 1cm is not very much considering that factory specs are just close approximations of where the bow performs the best. If you want to get back to 60# then maybe all you need to do is add a couple twists to the cables. This should bring the weight up without affecting the specs too badly.

I would say this. A string is a string when it comes to setting a bow to specs and those shops you were dealing with are a bunch of dick-heads. Most strings are made of virtually the same materials, usually Brownell or BCY products and none can hurt the bow. It's a shame you don't have better shops around and as you have found out it pays to be able to do things yourself.