To my understanding, the Pass Labs amps support AES48, the balanced line standard. This standard has two benefits audiophiles might like. The first is that it prevents ground loops. The second is it prevents the interconnect cable introducing a sound of its own. This means an inexpensive cable can sound as good as one that cost $1000/foot.
But to get that benefit, the preamp must also support AES48. There are tube preamps that do this and a few solid state as well. IME most of the high end audio market is ignoring AES48 so you get this argument that single-ended operation can sound just as good as balanced. But when you hear a balanced setup done properly you find there's no going back.