Thanks for your question about turning the B-60 into a 'passive pre'. The Bryston B-60 uses a high-impedance input buffer to isolate the source from the lower-impedance volume and balance controls. (This is one of the reasons for the very low noise floor of the B-60). This means you never really get all the way to 'passive', even by taking the signal from the tape-outs and going into an external attenuator. It does mean, however, that you can use a lower-impedance attenuator, like 5K or 10K, to keep noise low, and if you want to use the input part of the B-60's preamp section to drive another amp, you can use longer cables without losing HF energy.