3 basic questions about hooking up a soundbar

I have an LG 42" TV, an LG Blu-ray player, a FiOS set-top box, a Roku for streaming Netflix, and, as of yesterday, a Sony HTCT60 soundbar. Besides wanting better quality sound than the TV's speakers offer, I bought the soundbar in the hopes that it would boost the sound from the Blu-ray player. A TV volume setting of about 15 is adequate for the STB, whereas I have trouble hearing DVDs even when it's set to 75+. (Any ideas for dealing with that disparity would be most welcome.)

1. Is there any advantage to running sound through the soundbar *and* the TV speakers rather than turning off the TV speakers? Any disadvantage? (I don't hear an echo, so that's not a concern.)

2. Is there any advantage to running a separate connection from the Blu-ray to the soundbar, even though it works when I'm connected only to the TV? Might that give me stronger audio when watching discs? I can toggle between different inputs using the soundbar remote.

3. If I did decide to attach the Blu-ray, too, should I reserve the optical link for the TV since I use the STB more often, and use the digital or analog hook-up for the Blu-ray?

Thanks in advance!

Thanks -- that's helpful. Now that I look at my TV, I think you're right that the decision (for my question #3) is made for me: the only audio out is optical.

If others have thoughts about the low Blu-ray audio output, I'd love to hear them.