I wanted to add my $0.02 having just got my Pacifica today and (thankfully) stumbled upon this forum before pulling my hair out. First off, this thread saved me quite a bit of frustration because of the whole dual port thing. From my vantage point I couldn't see the port next to the BluRay player, so I probably would've spent a few hours trying to figure that out if it wasn't for the thread.
I did run into some problems with a 16GB USB key, but it has seen better times and is known to be finicky with anything other than a full-fledged computer. I decided to have a little fun, and I took my old Mac Book Pro SSD that I have in an external case and tried that out. There was no luck with it formatted in Fat32, but I switched over to a Windows 10 VM, reformatted it to NTFS, and it's working beautifully whereas the 16GB stick is stuck in the dreaded "Reading USB" state after working once. I unplugged and replugged the MBP SSD several times, and it was detected and browsable within a second each time. This is a 256GB drive, so it looks like the max potential for supported drive sizes is higher than the 128GB cue003 found. The system also didn't have an issue with chaptered m4v files.
I'm going to try setting up movies a few different ways to see what works and what doesn't. The less I can re-encode the better.