I'm confused by your dates. Do you need the CAI stopover in both directions? If so, I suspect that DL will try to price it as two separate award tickets. Remember, one way awards on DL cost the same as round trips.

Before booking on Aeroflot, check Russia's visa requirements carefully. Getting a Russian visa can be an expensive hassle. Even if you technically don't need one for transit, remember that this could render you stuck in the airport in case of IROPs.