For those who are interested, I just added new blog post on my site where I provide the schematics and board layout files on a connector for the J3A1 and J3A2 plugs of the Jetson TK1. It breaks out almost all of the important signals from those headers to a 40 pin 0.1" IDC header for prototyping. It also has schematics and board layout files for a level shifter circuit. I used the Jetson connector to hook up the touch screen SPI lines to an Arduino Due via the level shifter and I was able to transmit full-duplex blocks of data @ 25 MHz. I used DesignSpark to build the boards, and all the components have Mouser or Digi-Key parts listed so you can build these yourself if you want.
I am working on combining both of these boards into a single system now. I am also working on a new series of blog posts that describe how to get the touch screen SPI on the Jetson up and running.
Here is the link with the electronic board data:
http://neurorobotictech.com/Community/Blog/tabid/184/ID/10/Using-Jetson-TK1-connector-and-level-shifter-for-25-MHz-SPI-data-transfers.aspx
I have also updated the eLinux GPIO page to link to these files. Jetson/GPIO - eLinux.org
David