The gain cannot be changed by the end-user. I used to own the "high gain" version, which had 62db of gain. This should be used with MC cartridges of no more than .6mv of gain.
For more information:
http://www.anthemav.com/OldSitev1/pages/phono.html
For more information:
http://www.anthemav.com/OldSitev1/pages/phono.html