I’ve got the predecessor to the Panasonic you mention, it has a good picture and works reasonably well with Youtube. It does have one flaw with Youtube — you can’t fast forward within videos.
Netflix seems to work better on a dedicated device. I use my Xbox360 but a Blu Ray player should work fine. One advantage of the Roku is that it supports a wide range of other internet streaming options, including MLB.TV and a bunch of internet TV services.
There is no reason why you can’t hook up a Blu Ray by HDMI to your TV and run a digital out to your Bose. I’ve done that for years and it works just fine. They will all allow the audio to run through a separate digital audio out.
One unsolicited testimonial. Check out monoprice.com for cheap HD cables and stuff like HMDI switches.
I’m thinking Roku will be adding additional content in the near future too. If not for football games, I would cancel Comcast.