Pops, Interesting. Some of the best tweaks I have made involve PC's and Audio Magic Pulse Gens, which are supposed to cancel out EMI/RFI. I must be located in an area particularly subject to that problem. In the absence of strong RFI/EMI fields, I could see how a stock PC might be preferred. After all, that is presumably the PC used when the equipment was designed.
I't could be that since your system is not suffering from digititis, your tolerance threshold for RFI/EMI is higher. Who knows?
I tend to tune out ; ) the "don't confuse me with the facts, my mind is made up" crowd. As I and others have stated, it"s not possible to predict a priori the effect, if any, particular PC will have. It can certainly be a frustrating and expensive process.