The product works flawlessly with the OS that shipped with your machine and every one since until 8.6. We have an aggressive development program here at Newer that involves new products for USB, FireWire and Processor Upgrades. While we will do the work required to fix the 8.6 issue it must occur at a time that does not break timelines involving dozens of people and multiple companies.
Several months is an honest answer.
Maintaining compatibility with an OS that has undergone the huge changes of the MAC OS over the last year can be difficult. If in fact the next rev of the OS is before our update is released there is a good chance the issue will have gone away. I encourage you to consider the benefit of 8.6 over 8.5, the consensus of most people is that it is negligible. I would also encourage you to consider a NUpowr G3. They cost less than your current Nupowr and the G3 experience on a 1400 is amazing to behold.