Okay Stiles, now it's a bit clearer. First, using the speaker output terminals doesn't disable the pre-outs, so both can be used simultaneously. Next, using the surround amp channels on an HT receiver ordinarily sends only surround material to the speakers, but a mode usually called something like "all channel stereo" sends the front left to the left side and back surround channels and likewise for the right side. So, in that mode two sets of front speakers in other rooms could be driven by the surround amps in the receiver(with significant power loss unless very thick speaker wire, e.g. 10ga, was used).
Your description of what your sub is doing may or may not be the case(for most subs it isn't); the internal sub crossover doesn't have any effect on the output to main speakers connected through the sub, it simply rolls off the sub above the set frequency. Some subs have a separate filter on the output to the mains which rolls them off below a certain frequency(e.g. 80Hz), but in most cases it's just a straight feed of the full range.
No, don't count on using a Toslink connection for 100 feet; the losses are higher, not lower, than a coaxial cable.
So, you can use an HT receiver in the way that you propose, but if your main purpose is to get a good tuner, consider getting a separate one such as the Marantz ST6000 and keeping the rest of your setup the same if it's working well.
