Turns out that using more than one volume per disk connected to an Airport Extreme isn't a good idea. May explain some of my issues.
The AirPort Extreme (802.11n) and Time Capsule work with most disks that are not software RAID volumes (no more than one volume per physical disk).
[From AirPort Extreme (802.11n) and Time Capsule: USB storage device supported formats and protocols]
