The thread here has a couple of variations ... http://line6.com/support/thread/89338?tstart=0

Basicaly, if you are happy with the tone you use for rhythm and just need a volume boost then a clean EQ after the amp (e.g. Studio EQ with gain parameter boosted only) is probably the way to go.  Assign it to a footswitch and make sure that your amp can cope with the extra boost without running out of clean headroom.  If you run out of headroom then this method will just cause your tone to compress and may actually make things sound quieter and less dynamic.  Bear in mind that if you are running your amp through a PA then the boost may not be audible to your audience due to the way that the PA is setup for you.  Again you would need to factor in additional headroom.

The other approach is a boost before the amp.  Some people like a compressor here (though personally I don't like the loss of dynamics) and get good results. Other use an EQ boost including a mid frequency boost to make the solo cut through the mix more.  The Mid EQ is a good candidate for this one.

Much of it depends on the style you are playing.  Try a couple of methods and see which one works for your style and genre.