Modified PS Audio DL III DAC and jitter

I am considering a Cullen Stage III mod to my PS Audio Digital Link III. He claims that the jitter reduction is so significant as to be barely measurable. My question is this: if I use my Oppo 980 universal player, a high quality coax digital cable and the Stage III mod, can there be any difference in sound versus using a better source than the Oppo? If the signal goes through without interruption, and the jitter is effectively eliminated, how could the source player be a factor? If you believe it to be so, can you explain how this can be? I would rather spend my money on the DAC mod and then all digital sources, such as a computer, will benefit, but also want the best sound from CDs. Thanks for any and all replies.