With HP3, I recorded (using all the professional equipement I own) many takes of my best impression of Sirius Black, but the edit just didn't sound believable to me. So I'm nixing adding that line. Oh, to have the original film elements. Three words Alphonso! Just three words!
With regards to the Common Room scene, I tried to cobble together the intercutting footage mentioned above, but it didn't have the impact it needed as Ron awoke. For the audio, I tried mixing the "Come Out, Come Out and PLAY!" line with one of Ron's screams as The Grim dragged him beneath the Whomping Willow, but too much ambient noise (and music!!!) in the center channel kept me from getting a clean edit. It was a good idea, but hackey in the implementation. So I nixed the idea altogether and came up with a different approach.
I then took the unmolested scene and hacked a couple of large chunks from it. I removed Ron's dialogue and the McGonagall/Sir Cadogan/Neville dialogue from the scene. Placing it elsewhere, it now starts after Dumbledore's dream monologue and starts with McGonagall assuring the Gryffindor's that Sirius Black is gone but will probably try to return again. Cut out the Crookshanks bit between Ron & Hermione (because that comes much later in the story line), and have Hermione sit by Harry who is brooding into the fire about how Sirius was here, close enough to touch, and he could have killed him. Cut to blackness for about 10 frames as the music leads out, then cut straight to the falling leaf and Sir Cadogan's introductory scene. After this scene, then cut to Snape barging in to teach in Lupin's absence. This edit abutts the two deleted scenes together into one larger deleted scene and ties up the plot points introduced pretty nicely.
With regards to the Great Hall deleted scene after the first trip to Hogsmeade, I added a fun sound effect when Harry eats the candy that Ron brought back from town. Whatever was supposed to happen was left undone in the deleted scene, the palette open. So I searched for an appropriate sound effect that works extremely well.
I'm generating my 5.1 mix right now. After I clean HP2 off my drive, I'll mux and burn HP3 and then get started on the new book. Woo hoo!!!