Audio GD Compass 2 Upgrades?

I bought this DAC off this site about six years ago.  It has preformed well.  I understand that it is easy to upgrade but I have found almost no information about this product.  Does anyone have the schematics to this?  I have gone to the manufacturer's site and they do not have any listing for it even under Discontinued Products.  Any help or actuall experience with the Audio GD Compass 2 would be greatly appreciated!