Using two preamps with one amp via the fx loop

What I'm looking to do is run my preamp and main amp together but only using the power amp of the main amp.

What I want to be able to do is a/b between the two preamps but also have the ability to blend them when needed. So an aby pedal with a blend knob on the y section. I've got a boss ls-2 currently but in practice this will only alow me to a/b or blend but not both. Below is a signle chain using the boss which if this idea would work would be similar to a pedal I would have built.

Here is a signal path I was thinking of if I was using the boss ls-2 but it's only a mix of the two.
*(Bass > LS-2 Input, LS-2 Send A > Gallien Krueger *input, Gallien Krueger FX send > LS-2 Return A, LS-2 Send B > input of Pearce preamp > pearce preamp FX send > LS-2 Return B, LS-2 Output > Gallien Krueger *FX return.) Set the LS-2 to A-B Mix and use the knobs on it to blend the sounds and correct any level mismatch.

What I want to know is would this work? Would I be able to choose my pre a/b and when I want blend the two together?(not using the boss custom pedal will be made aby with blend)

Cheers guys

 

Currently a fusion 550