^^
It is not clear from the manual if the SUB out from the soundbar is already filtered at 80hz. If it is filtered at 80hz, then the LPF setting should be 12db/oct and then set the crossover knob to max. However, if the SUB out is not filtered, then you need to set the knob to around 80hz or slightly lower and LPF switch to 24db/oct.

As for the soundbar being too weak, you need to set the volume control knob on F8 from what you have now to 6 ticks to 8 ticks lower. This will bring up the relative gain of all other channels over subwoofer. My personal preference is center channel should be 2-3db higher because the location of center channel is dead center and that seems to make the perceive loudness to be lower than other channels.