Subwoofer yes seems an obvious choice.
Speaker impedance use the higher setting, here's an article explaining why
http://www.audioholics.com/audio-amplifier/impedance-selector-switch-1
80Hz crossover is a good starting point.
Sub delay (distance) doesn't always match up due to the extra processing time in the sub's circuit, you may need to adjust for that. Try this article
http://www.audioholics.com/home-theater-calibration/subwoofer-integration
I looked in your manual a bit and didn't see anything about the sound mode to use although I did see that there is a pure direct mode, do you have that engaged? For testing is your source 2.0 or something with LFE (like a 5.1 movie)?
In any case here's the troubleshooting entry:
"The subwoofer produces no sound
If the setting of the front speakers is "Full Band" and during
2ch input such as from the TV or music, the low range
elements will be output from the front speakers rather than
from the subwoofer. If you would rather output from the
subwoofer, make one of the following settings.
1. Change the front speakers settings to a setting other
than "Full Band" for the crossover frequency value.
The range below the frequency you specify will be output
from the subwoofer rather than the front speakers. We
do not recommend changing this if your front speakers
have good low range reproduc
tion capabilities.
2. Change "Double Bass" to "On".
The low range elements will be output from both the front
speakers and the subwoofer. This may mean that there
is too much bass. Do not change if this happens, or
choose option 1.
0
Refer to "2. Speaker" - "Crossover" (P37) in the Setup
menu for details.
0
When you play source material that contains no
information in the LFE channel, the subwoofer produces
no sound."