I did Rome on my own, and I hired a local guide for us who was also a local guide for ABD in Rome.
It strikes me that if you were to hire her, (she is quite reasonable), she could give you an in depth tour of Rome customized to you, and she would likely know the ABD itinerary so that you would not necessarily repeat attractions (unless you wanted to). She has all the “skip the line” superpowers that ABD has. Having said that, ABD generally does an amazing job of showing you the highlights, so you will see plenty if you just stay with ABD. PM me if you want her name.
Another thought is that Rome is an incredible city for pedestrians and for restaurants, which you can generally find just by walking around. You can easily spend a day or two just walking around and enjoying the shopping and the city.
I spent a week in Florence (not ABD) and there were still interesting things and museums that we did not get to. I would happily go back there. It sounds like it would be in the middle of your trip, so maybe not easy to add days there. Although there is a high speed train from Rome.