Try it with just the GSP cabs for a comparison. It's almost getting that "cabinet into another cabinet" cavernous sound a bit. I like the idea though. Something's not "opened up" for using the 11R cabs, they usually breathe quite a bit. Let it breathe if you're rolling off the highs. A second EQ to put back in some frequecies around 5k & 10k maybe, let it have a little noise up there. Maybe it's the mic choice. Put it on axis and try it if it's off. Once you get dual tracks, it can be night and day but sometimes you want to try that off axis position because it seems solid. You really have more to play with if you use on axis.