My Kensington dock is working! In Windows 8! Good grief, it's working... full USB3 speed, dual monitors, gigabit ethernet, and everything works just as it's supposed to. Turns out it wasn't necessarily a problem with the Kensington dock at all. Rather, I'm blaming Microsoft's USB 3.0 drivers for this one. I have two laptops I'm testing with this dock. Neither one worked previously with it, but the fix is similar for both:
Sony VAIO VPCSC1AFM:
This laptop has a Sandy Bridge architecture, and in Device Manager the controller showed "Renesas USB 3.0 eXtensible Host Controller - 0096 (Microsoft)". I was able to download the non-Microsoft driver from
Intel's web site here and install it (ignore the fact that it doesn't say "Windows 8" on that page - it works). Once I did and rebooted, the Kensington dock worked perfectly! Absolutely no problems so far. Easy.
Lenovo ThinkPad X1 Carbon:
This ultrabook uses a newer Ivy Bridge architecture, and so the Renesas driver won't work. Intel makes it difficult to install their driver in Windows 8, but it can be done by
following these instructions on Plugable's site. Once I did that, the ThinkPad worked with the Kensington dock, too. Again, absolutely no problems so far.
It's a huge relief for me, and hopefully things will continue to work fine. Maybe this post will help someone else out, because the problem was driving me crazy for days trying to find a solution.