I do have the balanced amp installed. It just not stay balanced mode even with the switch in balanced mode. It is like it slips out or my connector on the 901 has the pins in the wrong spots to make a good connection. Once my HD650 cable arrive I will see if it does the same thing.
The balanced mode, when I hold the connector to get it working sounds so much better it leaves no doubt when it is active and when not. Currently using the Songbirds in balanced mode, balanced amp.