Some mappers can map them but dont want to because they want to keep their name good and only put their services into something that is reliable and not going to go wrong and take an engine with it.
You may have a AEM ecu and have not had one problem but the limited amount of decent mappers out there for them certainly shows you why alot of tuners dont map them. I know probably the 5 best mappers in the UK and none of them will touch an AEM.
And the down grading comment certainly shows how much knowledge in this area you have.
Motec, link g3, and autronic is where i would be looking for a build like.
But it should always be choose your mapper and let them choose the ecu. If you want dan to map it get an AEM
Ryan.