So I whip out a FTDI-based multiport Serial USB Adapter....

[CeDeROM]

Just an idea - do you use "certified usb 2.0 cable" ? I had some
problems many times using non-standard cables..

Try using "certified cable". Try using different keyboard/mouse, maybe
they drain too much power from a single USB port that connects all
those equipment... try to see how much power do they drain alone... it
looks like a power problem.. but Im not an expert here and dont know
the USB internals in FreeBSD sorry :-(

-- 
CeDeROM, SQ7MHZ, http://www.tomek.cedro.info