I bought mine when I bought the mixer. They sound exactly like the mixer's converters. I have been very happy with the purchase because of it's usefulness. I wish it was already built into the DM though. As to its converters, this is from RedBus from another forum: (Actually it was the old TascamForums, Dec 7th 2009)
"IF-AN/DM uses the AK5383 converter (24bit/96kHz, 110dB range)
The DM-3200/DM-4800 uses the newer pin compatible AK5385A converter (24bit/192kHz, 114dB range).
The actual performance of the option card should still be equivalent to the mixer, given the performance of the op-amps in front of it. It's doubtful whether we'd get the 4dB of extra performance out of the IF-AN/DM by swapping chips...
RedBus."
Both are 24bit, which is a big deal. It's interesting that the DM's converters are capable of 192KHz. It must have been an executive decision to limit the board at 96. At the time, they probably figured, 'what's the point?'