Depending on the length of your cables you have a variety of preamp choices. However the balanced line system was conceived with the idea of eliminating audible differences between cables, so if it is done right, length is not an issue either.
Most tube preamps don't support the balanced standard, despite having balanced outputs. I have only seen one that does. If you can keep the cable short though, there are plenty of balanced tube preamps that will do the job. I think you will find that the move is quite worthwhile- your speakers may break in further but a good tube preamp will bring detail without brightness that so far has not been possible with transistors.
Most tube preamps don't support the balanced standard, despite having balanced outputs. I have only seen one that does. If you can keep the cable short though, there are plenty of balanced tube preamps that will do the job. I think you will find that the move is quite worthwhile- your speakers may break in further but a good tube preamp will bring detail without brightness that so far has not been possible with transistors.