FWIW the first balanced line preamp made was the Atma-Sphere MP-1 way back in 1989.
Whatever preamp you get, its useful to know there is a standard for balanced line hookup, known as 'AES48'. I've found over the years that most balanced line product offered to the home audio market does not support the standard.
In particular, in the balanced line system ground (the cable shield) is ignored- that is to say, neither the inverted or non-inverted signals have anything to do with it. In this way, the signal is more immune to the effects of the cable (meaning it does not have to be expensive to work really well) and ground loop noise is eliminated.
So its useful to know if the balanced line preamp you're considering supports the standard.