Ok, it's been a few years since I've owned an EMU, and maybe they've changed this since then, but my recollection is that the problem with the analog output is that it only has one input variable, namely, the analog input.
It seems to me that the analog input & output were designed to allow you to rescale a sensor on its way to the ECU. So you can tell it that for an input of "x" you want an output of "y" (along a 1 dimensional table) however you cannot introduce a second variable (such as MAP) into the equation.
So you could run the NBO2 sensor through here and scale the table to prevent the signal from ever rising above, say, 0.6 volts, but that would prevent proper closed-loop operation from ever occurring- the ECU would go to max positive fuel trim and stay there all the time (and probably throw a code.)
We need to be able to allow the normal sensor signal to pass through to the ECU all the time, except when we are in a situation where we're deliberately adding positive fuel correction with the EMU. So to do that, we need an external switch, controlled by the EMU, which can select between the actual sensor output or a simulated voltage.
I did some searching and found this little writeup that I did a while back: http://www.miataturbo.net/showthread...d=1#post204086
It describes the construction of a little external box which is controlled by the EMU's VTEC wire by way of the Aux Output Map.