I use a custom built converter unit. All the sources go into an ultra-high quality switch which then feeds a single ended input of the "volume control unit" (it has no gain so isnt really a preamp). This unit contains a single ended to balanced converter, a balanced high quality stepped attenuator and three pairs of balanced line drivers. This combines the benefits of passive preamp approach with the incidental buffering of the balanced drivers and converter so that it does not suffer passive disadvantages. The slight signal degradation caused by the electronics is more than offset by the benefits of using the Brystons in balanced mode. I then use three pairs of balanced xlr cables to connect from the volco to the pair of 4b-st and pair of 7b-st that I use to tri-amp mb2s. This unit sounds much better than using the bryston preamp with a set of y-cables. I had the unit custom made for about £500, not counting the switch which was about £150.
Nick.
