I have recently watched and read some info on this.
Good idea to put the studs up on the block walls. Then put two different types of insulation between every stud alternating between each stud. One dense insulation and one less dense. The thought being one will absorb the lows better and one the highs better.
Then put two layers of dry wall so the seams don't overlap. A good tip also is to leave a gap at the bottom that you can run wires through, then just put a base board over the gap to cover them.
If you want to go all out can put in a floating floor, but then things get a bit pricey.
You have the worst size room you could have for sound ... a perfect square. Use what your doing about the cinder block to make the room NOT a perfect square. This will be definately the most bang for your buck in making your room sound MUCH better.
