Looking at the build pic and reading what you're trying to do here, I think that the Frames is a poor choice with as few modulation sources as your build has. Also, the Pittsburgh...while it's a good mixer...won't do what you want, either. And as for attenuating the output (which I'm a bit confused about your description of here), it doesn't matter what mixer you use, you have to attenuate an output to a line-level input because synth-level signals are quite a bit hotter than regular line-level.
If I were facing the same problem, I would first go with a different mixer altogether, namely one which has its main functions under CV control, but which doesn't have extra complexities. The Frames is really more intended as an audio signal "morpher" than just a mixer, and the Pitt module isn't as automated. Instead of either one, have a look instead at Qu-bit's Mixology, which is a four-channel mixer with CV over channel level, pan, and effect send and the additional utility of channel mutes and solos.
BUT...and this is pretty critical for making a build succeed overall...you desperately need more modulation sources. I don't see any additional EGs or LFOs, which are major bread-n-butter modules in of themselves, that can be dedicated to envelopes for your level VCAs or effect send VCAs or LFOs for panning and most everything as well. Plus, even with this different mixer, you will still need some sort of output level attenuator/control to keep from running your mixer input into immediate distortion.
At the basic level, this isn't a good build at all. Your Moog devices really should stay in their own OEM cabs if you're building in 84 hp cabs, otherwise they're hogging space that needs to be there for other things. There are no VCAs (linear or exponential) outside of the Moogs, nor any LFOs or envelope generators beyond what the Moogs offer. I would strongly suggest that you stop what you're doing with this, step back, and take some time examining other builds by experienced users as well as classic modular/patchable instruments to see what those people or companies are/were doing. Take some time to go through the forums here, also, plus at other sites such as Muff Wiggler, Synthtopia, etc to get a more concrete idea of how to proceed. Do the very necessary research before continuing, because modular can be a very effective way to create...but conversely, a very effective hole down which money gets uselessly thrown if one has no clear idea of what they're doing. Sure, they look cool and all, which is why a lot of people right now are drooling over them, but without a clear understanding of what you're doing and why you're doing it when creating a build, it doesn't matter how cool it is, it'll just be a waste of your time and money.