ResMed VPAP Auto Mode options?

I'm seeing a different doctor tomorrow, so in preparation I wrote down the settings on my machine. I don't understand several items: Mode, Easy Breath, Ti Max, Ti Min and Sleep Quality. But the one that stands out is MODE. It is set to "S". The other possible MODE settings are "V Auto" and "CPAP". The Clinical Guide describes the Mode setting as: "Sets the therapy mode depending on what modes are available on the device." That's all. The Guide that came with the machine shows a few screens, but never mentions Mode.

I can imagine the CPAP setting sets the high and low pressures (mine is set for 18 and 15) and does not adjust them automatically. What do the V Auto and S settings do?

Which of the three settings should it be set for me?

My sleep study AHI was 68.0 and while using VPAP has averaged 3.26 for the past 6 months, with numerous spikes above 3. My symptoms, daytime sleepiness and falling asleep while reading or at the computer, have not improved during the 6 months I have been using the machine.

3 modes of operation for the S9 VPAP Auto.

1....CPAP mode..plain old cpap mode with EPR just like what is offered on the Elite.

2....S mode...this is a fixed dual pressure mode. So two separate pressures or bilevel pressures but they are fixed and won't auto adjusted.. EPAP and IPAP never vary from whatever the settings are.

3....Auto mode...Dual pressures that can auto adjust depending on what the machine thinks it needs to do. So Bilevel pressures that can vary depending on what the settings are set to allow for variances. Pressure support is fixed though.