BTW, one last piece of information, from a BBS back in 1997, when someone asked about the XP-80 DACs. More recently the Burr-Brown PCM69au's been replaced by the PCM1800, which are 20-bit. Same logic applies, though. Here you go:

From: WeAreAs1@aol.com
Date: Mon, 6 Oct 1997 20:44:56 -0400 (EDT)
Subject: Re: Re: [jv1080] XP-80 D/A convertors

The JV2080 does not have 20-bit D to A converters. It uses Burr-Brown
PCM69au converters (the same ones used in the XP-80 and several other
models), and these have 18-bit resolution.

It is important to understand, however, that the JV/XP series all have 16-bit
*data resolution*. Running this data through an 18-bit converter does not in
any way increase the resolution of the data. The additional two bits will
simply remain unused.

There is a slight sonic improvement when running 16-bit data through 18-bit
converters. This improvement occurs at the very lowest signal amplitude
ranges, such as decaying note fade-outs and reverb tails. The additional
bits will effectively correct for possible amplitude quantization errors for
signals that are at the lowest possible amplitude or are approaching zero
amplitude. Whether this effect is actually audible in the real world is up
to question.

Anyway, don't get all worked up about 18-bit this and 20-bit that. The JV/XP
is a 16-bit sample playback machine, and no amount of additional resolution
at the converter will be able to change that.

BTW - in answer to the previous question about the conversion of the effect
proccessor data: All signals in the JV/XP are digitally mixed within the
synth's tone geberator and DSP chips before going to the D-A converters.
There is only one generation of D/A conversion.