It would require more than just changing out the DAC chip. It would also require writing completely different software for the player, software that was coded directly to the new DAC. And from what I understand, these DAC chips aren't exactly pin-for-pin drop-in replacements for each other. A significant amount of hardware engineering would be needed as well.
From what I remember, there is no provision in the existing hardware for multichannel audio, beyond the SDATA 1 and 2 lines. IIRC, there is no DAC chip in the Empeg per se. It is built into the DSP. You would have to completely bypass the DSP and all of it's features and of course rewrite the software as Tony suggests. DACs are rarely drop in replacements for one another. The one referenced in the original post in this thread does not have particularly good channel isolation and requires separate SDATA lines for each stereo pair, which of course are not available in the stock Empeg. Making eight separate channels of audio work well inside the Empeg or similar device would be quite a feat. To get really good performance would require at least 4 separately packaged DACs.
Anyway, as Tony said, it's not really worthwhile to attempt given the complexity involved.
Stu
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If you want it to break, buy Sony!