If you select the DVD input, and select optical inputs opposed to the 7.1 inputs you can select stereo as a surround mode. This mode appears to put a very weak base signal to the sub.
Which makes sense - we're in the digital domain (optical input), and the 1070's bass management is in effect.
If you press the bypass button it has no effect.
Also appropriate, since there's no analog input to fall back to (unless you have stereo analog cables run from DVD player to the 1070).
If you select the 7.1 DVD input mode and your bass management is set "bypass" then your surround setting simply says "bypass" and you can't change it to anything else.
That makes sense - the signal is staying in the analog domain, making surround processing impossible. The same should also be true when the switch is in the "HPF/LPF" position (which uses the 80Hz analog crossovers but still keeps the signals in the analog domain).
If you select the 7.1 DVD input mode and base managment is set to digital, your surround options are limited to digital, dolby +PCM PL11x-C and M.
This is pretty cool, actually - it suggests that in addition to the quad crossover bass management, you have the option of using the 1070's Pro Logic IIx processing to create surround back channels if you wish to.
Going back to your earlier post, you reported having the switch in the "HPF/LPF" position and experiencing bass management when using the bypass mode with a CD. Did that occur with analog cables run from a CD player to the 1070's CD input?