Same with me. NSLU, Maxtor One touch drive. Spins down & back up again just fine when the SoundBridge accesses Firefly.
But then, i don’t use iTunes much either.
What i have noticed, when connecting iTunes directly to the library on the NAS, is that it doesn’t wait long enough for the drive to spin up.
In this case, if you’ve mapped the network share to a drive letter in Windows. The drive will often not spin up at all.
If iTunes is given the actual path to the network share then it will spin up the drive.