have you turned the master volume down?  That's where I'd start, unless you've done that already.

you can download a copy of the manual, via the support link at the top right of this page.  But here's the link for you: http://line6.com/support/manuals/

You should be able to work out what settings are stored within the presets using the blink out method, and then turn down the channel volume (which is the volume setting that's saved in the preset).  The master volume and presence controls aren't saved in the presets, they're 'master' controls that react to where the knobs ont he amp are positioned.

Hope this helps for a start

Rowbi