modifying a Grant Fidelity TubeDac-11 with a ESS ES9016K2M SABRE32 Ultra DAC chip

Hi All, I have no idea of how and what to do to modify my Grant Fidelity TubeDAc-11 with a ESS ES9016K2M SABRE32 Ultra DAC chip. I have the SoundBlasterX AE-5 sound card installed on my desktop but after connecting directly to the AUX connection on my Sansui AU-9500, which I'm using as a pre-amp, the sound sound is good for about 2-3 minutes. After this time, the sound become garbled, more like a tape recorder playing a tightly wound tape. Music is slowed down then garbled.

So that's really the reason to modify the Grant to accommodate the better DAC chip and rectify the sound quality problem. Is this something that is doable and how much expertise does one need to have?
Probably a bad idea. Likely better to fix the old dac, or else buy a new one.

Why? The problem you are having might not have anything to do with the dac chip, it might be something else entirely, and maybe it could be something you were not planning to replace. Also, its not easy to replace one dac chip with another just arbitrarily. You may pretty much have to redesign the whole dac board in some cases.