The specs indicate that the 600A will work fine when installed in series in the cold water supply to the cold faucet. You'll need to get the proper hardware to make the connections. If you're smart you'll allow for a graceful retreat back to the way the plumbing was if your don't like the filter or it fails or needs service. Is there a particular aspect of your water quality you don't like because these filters will only do so much.

Why do you need both filtered and unfiltered water? That's complicating your decision needlessly. ALso, with only 36" of counter space and a under counter refrigerator, that only leaves a 12" cabinet for a bar sink. That's NOT doable. Even a tiny 12" bar sink needs a 15" cabinet. And a 12" bar sink IS tiny. Take a look at the actual interior measurements for one before you lock yourself into something completely unworkable.

Jenny, Any update on what you ended up doing? I installed a whole house softener for hard water issues, but I have odor issues (sulfur and chlorine mostly). I'm leaning toward adding a charcoal filter before the softener. We also have RO in the kitchen and wet bars. Also, you could always just have another hole drilled for the RO faucet without replacing the granite slab. If you have an undermounted sink, the new hole is all you need. What did you end up doing?

How about this Pfister GT529-FLC which combines a regular kitchen faucet (hot and cold) with a filtered-water, cold-only faucet (you push the lever back for filtered water)? Not bad looking in my opinion and eliminates the need for two faucets.