Running two preamps using one amp via the fx loop

[victor5string]

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?

Cheers guys