Using preamp for sub instead of Main L/R

So I bought an Adcom GFA 555 II Amp today, and rewired my Marantz SR8200 to be using the sub pre-outs from the receiver where I previously had my fronts (Totem Mites) wired through the sub and into the receiver as Main left and rights.

Well anyway, I think the fronts sound a lot better now, but the sub (Totem Storm) sounds really weak now. I've got the receiver set to acknowledge the sub, and treat the Mites as "small".

Changing the frequency filter on the Storm, as well as the gain, does not return the bass to the levels I had in the previous set up.

Any thoughts on how I can fill in the low end again with a settings reconfig? I can't think of how to rewire back to my original configuration with the addition of the amp...

Thanks