What gives Crestron a bad name is people programming their product without training and support. Crestron offers outlets for Certified Programmers for every state on their website.
For the OP, adding a iServer to Adagio with Systembuilder is not really difficult, but you will HAVE to have a login for software and firmware. Also, you will have to be careful of what this system is doing because without the original program you will be starting from scratch. If the program needs to be written in SIMPL, you can probably tell by the equipment list. And Adagio and SIMPL can be a little rough, so be careful.