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So here's the setup: I am working with a piece of cello music that layers bowed cello with plucked cello (filling the role of percussion). The director is asking whether I can independently control amplitude on the plucked and bowed cello that is laid in together. My answer was a very tentative "I'll see what I can do."
My current thoughts have been to either use an RTA (I have SIA SmaartLive and a couple plugs) to locate the fundamental and then just multiply for the overtones and notch eq them in the box. I have also considered just pulling out an outboard parametric and try to notch out or gain the fundamental of either the bowed or plucked, but probably the plucked...plucked seems to have less frequency spread.
Any thoughts? Are there any other strategies not relating to EQ, or do you think I am going about this backwards?
+1 on asking for separate audio tracks. You'd have an easier time with EQs if they occupied different ranges of the audio spectrum, but you're talking about cello over cello. It's going to be nigh on impossible to get any separation for one that doesn't affect critical frequencies for the other. Maybe if all the two cellos were one rhythmic note each for the entire piece, but I highly doubt that's the situation you're working with.
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You could try a multi-band compressor. I've used mine succesfully to help bring up parts of a mix that are too low, and push some down. That way you can seperate and lower or raise sections of the frequency spectrum. It works for subtle changes and adjustments. I don't know how drastic of a change your director is looking for.
Other then that and clever EQ that you've discribed there's not much you can do.
I second Ryan's suggestion of asking for the original tracks. Re-mixing it to work with your soundtrack would give you a better product in the end, not to mention easier.