To me it sounds like you are facing problems with your CDs. Either you got ones that are for specific models, or your media are corrupted? As you could update from 9.0.4 to 9.1 right now, we know that it works in general. If you have a well working "reatail" CD of 9.1 it should install directly at your 7600.
Anyways the 7600 is not supporting 9.2.2 officially . You'd need os9helper for installing 9.2.2. but unless you have an ATI card and need that specific latest ATI drivers for 9.2.2 or one of the very few programs that requests 9.2.2 there is no reason to not stay with 9.1!
Also do not forget to use the latest XL8 MachSpeed control. Btw. which MachCarrier version do you have?