Shawnz28 - While it is theoretically possible that it will work, the odds are pretty good that it will not. The vast majority of people who try this find that the .1 increments are insuffecient to tune the wavebox. Realistically, a minimum of .01 increments would be required. So, for 1 in 10 it probably does work.
The 6091 is an analog controller so allows an infinite range of increments.
Anyways, camp, you need the Y adapter because both the 6091 and Apex cables are male. The Y adapter is female on both sides. The Y adapter allows you to connect the two cables together. It also allows you to control two waveboxes if you need too.
At the risk of getting in trouble, google this:
abcha0s Neptune Apex controlling Tunze Wavebox
Take a look at post #117
I can't guarantee that it's supported by Tunze or Neptune, but I can assure you that it works?