Unfortunately, many DAW components (both hardware and software) have some difficulty when it comes to processor upgrades. Back in the day, when the company I worked for was configuring many DAW systems (all Mac based) from the Nubus architecture thru the PCI based G3s and G4s, it became very apparent that this little extra twist (a 3rd party CPU upgrade) could really play havoc when trying to get a system up and running correctly. There were combinations of CPU upgrades and interfaces that did not play well together and combinations of DAW software and CPU upgrades that did not fully function correctly.
in the end, we gave up on third party CPU upgrades for DAW systems since it started to feel like we were configuring PCs, not Macs… too much shit to remember of what worked right with what revision of what. So we told our clients to stick with unmodified Mac systems and just pay a little more if more speed was needed. Apple did a pretty good job, IMO of matching overall performance with bus archiitecture, CPU speed, and stability… Now, I am not saying we wouldn't take a piece of shit QS 733 CPU (with only 256 K Cache) and upgrade that baby with a Dual 867 QS CPU… I am just saying we avoided the 3rd party variable that would have us up till 3 am trying to figure out what was going wrong with the system.
I think the main problem is that most CPU upgrades are tested in the arena of real world statistical calculations and benchmarks… and yes, most applications worked just peachy, but when it comes to DAW software and audio interfaces (all tested on stock macs), this is a different thing all together. Some DAW software and audio interfaces rely on things that inherently original apple, and a third party CPU is like a alien unknown variable with CPU speed software introduced and a different balance of Bus vs CPU.
I am not saying it is NOT possible to have a great running DAW with a 3rd party upgrade, many have achieved this… I am just saying it requires more research than a stock system, try to get a "Known" tested configuration that works for Mac model, CPU upgrade, DAW software, and Audio interface. That is why I think many, like Mactron, went the over clocking route… it is still the original system, but just revved up a little faster, introducing a little more heat and a few other variable, but overall, the systems "looks" the same to DAW components.