I already wrote luis, but I had the same questions. Obviously EMU was not willing to give up the schematics. SO, I did the next best thing.
Did some research, found the TI PCM4202. SNR 118dB.... Pin for pin is the same as the 1804 but with some slight differences, I guess a different voltage reference.
I had a EMU 1212m I picked up the EMU 1820 audio dock alone for $20 for the increased number of inputs and the monitoring options. I was disappointed in the sound quality compared to the 1212m, which has the AKM A/D and the better D/A on the daughter card.
Anyway, I did the swap, sounds good, I am noticing a certain clarity with the 4202 that just wasn't there with the 1804. The recording I have done with the 4202 installed sounds much more like the recording I was doing with the 1212m.
Also, any 1820m users that also have the 0202 daughter card? Are the drivers the only thing holding us back from using both to give 10 inputs and 2 more excellent outputs?