If your BAT preamp has available RCA inputs, use them. There is most likely no SQ advantage from using the balanced XLR input with an unbalanced source. There is a slight, insignificant increase in gain via XLR, but your signal will also negotiate an extra adapter.
If you need the extra RCA input, I've used the Cardas Clear adapters on Ayre equipment with good results. I think BAT also makes some adapters for its systems.
If you need the extra RCA input, I've used the Cardas Clear adapters on Ayre equipment with good results. I think BAT also makes some adapters for its systems.