Having just (only marginally) dealt with numerous supply lines running across the ceiling of my room I can certainly say that it's been quite a challenge. I think the thing to keep in mind is that no matter what you do, you have a hole through your upstairs floor to deal with where the vent comes through, so the celing joist space no longer becomes a sealed area.
I eventually did a single layer of 5/8 drywall, decoupled from the joists. I built backer boxes for the lights, but didn't go through the effort of dead-venting each vent hole that supplies air to my room. Instead I just put a few layers of drywall just above the openning, which should help reflect some sound back down to be absorbed before hitting the upstairs floor.
For the upstairs supply lines, I wrapped them in Safe 'n Sound insulation so that any sound getting into the vent has to first go through a full layer of that. Given that I'm still left with the gaping whole to deal with, I felt that was in line with the overall effectiveness of what I was targetting. My concept was to bring the whole construction to a certain acceptable level, and try not to go overboard on some areas while negating other weak-links that would leave me no further ahead.
The result? When I get my equipment set up (painting now) I have enough wiring in the room and the house that I'll actually be able to run ETF to show what it sounds like in my living room directly above. It went from "I can hear every word of your conversation downstairs" to conversations being inaudible. Music played fairly loudly though, can still be heard. The sound of the furnance will mostly drown it out, but if it's quiet and you listen (esspecially near a vent) you can certainly hear it faintly. I would say that for me watching at "reasonable" volumes, the sound going into the living will be persceptible but not distracting. Watching at "I'm showing off my system" levels, it'll definitely be heard upstairs for me.
All of that is just to give you a feel what you might be in for. The DD/GG will help for sure but I think to get maximal isolation and near-silence upstairs, you need to consider basically dead-venting each of your upstairs registers. I did a large dead-vent for a CA return in the rear of my room (the rear wall being much more of an isolation priority for me), and it works absolutely wonderfully.
My last bit of advice is be prepared for a very, very, long construction "delay" as you do all of the dead-venting, backer boxes, etc. It's amazing how many isolation issues and weak-links pop up once you start wrapping your head around it. Another one for me was the joist space above my room walls being open to the rest of the house as well; again, you're left with only 1 surface to block the sound and it's no longer a sealed container concept. I bet over half the man-hours into my room was dealing with isolation, and you can see that I went half-assed on a few aspects of it. I could probably have built a normal room for about 60% of the cost...
P.S. Great idea building the right side soffit to match; I did the same thing and I'm very pleased with how it turned out. Turns a liability into something that looks like an intentional feature.
P.P.S. One last thought... It looks like your riser depth is planned at 4'6" with a 2' aisle, which is also what I'm planning for aisle depth. You have recliners in your diagram though and I think you may find that 2' of aisle is insufficient for a recliner. This thread details how a 5'6" riser was re-built at 7' depth because he felt that he needed more aisle space for the recliners. http://www.avsforum.com/avs-vb/showthread.php?t=1103345
If you're not doing recliners in the rear then I think you're set at the 2' spacing.