Okay, now I see that after replying to your other thread that you did have more questions. Keep in mind that since your 2235 doesn't have a separate output for low frequencies to the sub, it's going to be sending the same signals to the sub as go to the main speakers. Therefore the same controls which affect the signals to the mains have to affect the same ones when they go to the sub. The bass/mid/treble tone controls do this, although of course the mid and treble won't make a meaningful effect on the low bass frequencies which the sub will play. Likewise, when you increase the volume to the mains this simultaneously increases the volume to the sub, so there's no need to change the volume control on the back of the sub.
This makes your question 2. pretty much moot, but as I said in your other thread, the 80Hz setting on the sub would provide a reasonably good blend with the M3s, so it shouldn't be a major concern.
