Is this museum still open or has it's statues been moved to Palazzo Massimo as part of a consolidation of the National Museum of Rome? I looked it up in Rick Steve's Rome 2014 guide book which seems to suggest that many famous statues are now to be found in the Palazzo Massimo.
I agree: it is a delightful building. Have been there twice. It was recommended to us some years back by a friend who lives in Rome, who told us not to miss it. We had never heard of it.
@David about Rome, I agree - good spelling mostly; it's Crypta Balbi.
Each of the four has different aspects of Rome's history.