Horizons,
The Panasonic SA-XR45 can be used in "Party" mode where the same signal is sent to front and rear surround channels. If you set them both to large, there will be no crossover engaged. If either is set to small, then the 100-200 Hz crossover comes into play. If you turn the sub to on, then the 100 hz crossover will filter out the highs from the sub outlput. It will still allow all the other channels to play full range. When in "Party" mode, the rear channels are reversed, L becomes R etc. Take this into account when wiring up your speakers.
This can also be done on the SA-XR50. The set-up is a touch more complicated but the same thing can be accomplished. I have yet to see a SA-XR70