As I recall the 950's analog input, the subwoofer always gets a combination of the LFE signal and the summed low-passed signals from all other channels. The rear panel switch only controls whether or not a high-pass crossover is engaged for the full-range channels. (Thus when the switch is "off" you have a potential for "double bass" because the sub still gets audio below 80Hz from the full range speakers.)

There are a couple possible explanations for the sub channel not getting anything. One is a hardware defect. Another is a bad cable between player and 950. Another (and the one that I'd focus on most closely as it offers the greatest opportunity to fix things readily if it is the culprit) is the player setup. Make sure the sub is on and all of the speakers are set to "large", then try that S&V DVD's test tones again. Another good test would be to move some cables around: hook the player's right channel output to the sub input on the 950 and see what the sub does when you play a test tone through the right channel. Also, the 950's test tones aren't going to be useful in diagnosing this, as they are created in a completely separate part of the processor.