What is there to risk. I'm actually not doing anything to the furnace. Just moving the return that's in the basement to the other room. My questions are how best to get controllable temperature in there with proper ventilation. I've read through both of your forums quite a bit to help me with this, and both of you asked a lot of questions too. I learned you can never ask too many questions, sorry if I seem to be "going in circles" but I just want to make sure I understand everything 100% before I get in to it which is a good thing. Which also means based on the wealth of knowledge that I have gathered, I can make a common sense decision on whether to do it or have someone else do it. Not everyone on this forum has thousands upon thousands of dollars. I actually do projects on this theater as I can afford them each week. If I cannot afford raw materials one week because of bills and whatnot then raw mats don't get bought and I work on something cheaper or caulking etc. This allows me to get quality information from you guys who have been there, done that which i appreciate immensely.
Here's how I look at it. I'm going to need a supply in that room no matter what, which means a supply vent, which means a hole in the wall as I don't have the ceiling space for a soffit. So based on that, I'm going to actually test what works and what doesn't instead of just guessing and hoping. Going to start with the supply that's in there now. Wait until the room is 100% finished and have people over to watch a movie or 2 and see how it handles it. If it handles it well then I leave it and soundproof the line accordingly. If it has a hard time keeping up, then I remove the current supply and look in to a mini split system in the adjacent room with a dead vent supply to the theater room, that way I can control the temperature from the seat of my couch with the remote. I plan to line the studs accordingly, just in case I'll be putting a deadvent for a supply in the future. The return will be a deadvent regardless.
Either way the furnace will be untouched.
Also, I did a temperature test in the basement today. I stood in the furthest corner of the theater room with both supplies open to said room. It rose the temperature 6 degrees in the 4 minutes it was on. I closed one supply and the same thing from the same spots. It rose the temperature nearly 6 degrees(5.6) and pretty much matched the same temp with both supplies open, again on for 4 minutes. So I think I can get away with only 1 supply in this room as it is a small room(11.5' x 17.5').
I say all this based on your guys' help so thank you, and know that this HT is not going to be some hack job, I think i'm annoying enough with my barrage of questions every day as proof of that lol.