The reason you would want "pass through" in a two channel preamp would be to conveniently use it in a home theater system connected to a multichannel receiver so you could use the presumably-higher-quality preamp and its associated power amp(s) for critical music listening of two channel sources, and use the same amplification for the front L/R channels for movie soundtracks using the receiver to handle the Dolby Digital or DTS and to take care of the rest of the channels' amplification. With the "pass through" feature in your preamp, if set up properly, you would not have to rearrange the interconnects or diddle with the preamp's volume control when playing a multichannel source through the receiver.
As stated above, the "bypass" mode give you a direct analog path through the preamp, avoiding the possibility of additional distortion introduced from digital processing. Very useful for playing vinyl LPs, for example.
The beauty of the Bryston SP2 is that the pre/pro has a built in two channel analog preamp section equivalent to the BP26, so you can hook up the SP2 and use it in bypass mode for pure analog, or have it process and distribute your multichannel sources using its full digital capabilities -- "pass through" to the front two channel amps is a moot point since both the high-quality two channel and the multi-channel capabilities are both "built in" to the same unit.
Burke
