I have the same Problem with my new B04 - assuming that the device is a Pogo v2
I already tried a serial connection (wich works fine on my Linksys NSLU Device), but there is no output in my putty terminal. In your link above it is mentioned that the broken serial connection is a result of the broken uboot. If my serial connector works I can confirm it.
My serial connector is just the old "RS232 connection without a kit" (
http://www.nslu2-linux.org/wiki/HowTo/AddASerialPort) (not USB DKU-5 or CA-42 cable!!) but i suppose it doesn't matter.
I also have the original uboot dumb. Any idea how we can further investigate the jtag connector? I have no experiance with jtag conncections except modifying an xbox360. But this seemed to be quite simpler.