Manual Audio on Flagship Handycams (e.g. HDR-CX760v)?

[Kris Kohuth]

I'm considering one of the higher-end HDR-series camcorders (cx760v, pj710v). I shoot in natural/uncontrolled environments, and need the ability to 'lock' the audio levels. I've downloaded a user manual, and get the impression that this isn't possible. So, does anyone know:

-Can the Automatic Gain Control (for audio) be defeated?
-Does switching to manual control (via the menu) offer anything beyond the two settings of 'Normal' and 'Low'?

Thanks.