I'm thinking that the Grass Valley ADVC-HD50 (mentioned previously) is the solution for me. It has HDMI in, FW400 (bus power) out. So I can connect the NX5 via HDMI and then to my Macally PHR-S250UAB external drive which has both a FW400 port and 2 FW800 ports, then to my Macbook Pro's FW800.
Even though I am still salivating over the Teradeck Cube, my set up would be a static enviroment so I'll have to save that purchase for another day.

I found a review for the ADVC-HD50 on B&H. The guy said his AVCHD Panny worked just fine:

Grass Valley ADVC-HD50 Real-Time HDMI to HDV Converter 602227 -