Let me see what I can do here...

Two-channel analog bypass (stereo bypass): In this mode, the signal from any stereo analog input is passed directly from input to volume control and through the pre-amp outputs. At the same time, a copy of the analog signal is converted to digital and passed to the 950's bass management module. If the main speakers are set to "small," the bass management module routes this digital signal through the low pass crossover and creates a subwoofer signal, which is then converted back to analog and sent to the sub. If the main speakers are set to large, nothing happens.

Six-channel analog input: This is a separate and purely analog signal path through the 950. The subwoofer output always receives a combination of the LFE input channel and the output of 80Hz low-pass crossovers from the five full range channels. The crossover on/off toggle enables or disables 80Hz high-pass crossovers at the five full range channels. This is all sent to the volume control; I do not recall if the 950's channel delays are applied (I believe they may be), and as you note the bass and treble controls (which I don't think I've ever touched) are applied.

Fixed 80Hz analog crossover versus adjustable digital crossover: Which is better depends at least in part on your speakers. If 80Hz is the preferred crossover point for your combination of speakers and sub, we are talking about the difference between crossover slopes and fundamental design characteristics (which for well designed crossovers should yield comparable performance). If you need a significantly different crossover than 80Hz, then the digital crossover obviously is better.

I'm not sure which signal path might be classified as the "purer" route for stereo analog sources. If you prefer the soundstage when using the six channel analog input, then I would say that's the way to go.

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