I got that info from the Blog of the "One that should not be named", he tested a bunch of them, and this Op-Amp showed as the best for Headphone usage, and one of the cheapest in his tests.
I have already arranged to buy a JDSLabs that was being sold by an user here at Head-Fi, so I will have a cMoy to use with my HD558 while I wait for the ODA to come out. It uses an OPA2227, which isn't as compatible with different types of headphones as the 4556 according to him, but mine should have no problem.
I will let you guys now if I notice any improvements when the unit arrives here, should take a while.
that explains it. I'll leave it at that, thanks