Battery Boxes - Brien, I'd PM you but I can't.
I agree that especially with the newer Sony recorders that don't have a low/high sensitivity switch like my MZR30, an external attenuator is a pretty good idea.

Now, about that bias... (technophobes avert your eyes now...)
In an external battery box, it's perfectly possible to supply a constant voltage to the electret, then feed the audio though a capacitor to a conventional volume control pot.

Furthermore, if you put a DC blocking capacitor between the ground end of the pot and the actual ground, you can supply bias from the recorder at all levels of attenuation, no battery required. I've done this when making Microvox battery box clones for my own use.

The voltage across the electret will change a bit as you adjust the volume control, but that's a side-effect. The pot is attenuating the audio signal in the usual way.

With my MZR30 in the low sensitivity position, the auto level control is actually quite good unless I'm recording a loud amplified band. For any acoustic recording, it hardly ever cuts in, but I can be confident that it will not over-record. I have considered making a 20dB pad for it, with the ground cap as described as above so the electret still gets most of the bias voltage.

(ok, it's safe to look now...)

Anahata