I did look at that section, as well as go through the support forum. I was just hoping that there were other alternatives other than the Boss aux switch, and I was wondering about the issue that someone told me that by using the expression with the aux, and only getting toe/tip down position- so my understanding is that it's either 0 or 100.
There are other alternatives to the Boss switch. The guys at Barn3 released a really neat product for the H9 very recently which is 2 aux switches with an expression pedal jack: http://www.barn3.com
If you just want to use it as an Aux switch, then you can assign functions to the two switches (using Ring and Tip + Ring).
If you want to use it as an Aux switch plus expression pedal, then you can only use one aux switch at a time and you can plug an expression pedal into the jack on the side. The expression pedal will hit all of the values from 0 – 100. In this mode you can also press the 2nd aux switch and it will control the expression pedal patch but just go from 0 to 100 and not hit any values in between.
What's neat about this product is that it sits flush with the H9 and allows you to easily go from a set-up with 2 aux switches to a set-up with an aux switch plus expression pedal without needing to fiddle with Y cables.
If you want to get one of these, I'd use one of the expression pedals we recommended in the above howto guide.