It probably doesn't matter how you build... we used 24ytong and have already had a party or two in there. If you party from October to March, you'll never really get the place warm anyway. Just turning on a fan and working out doesn't work with either option.
In terms of sound, you didn't really notice much in the garage. You just have to decide what's more important to you:
Kalksandstein
- better sound insulation
- more space in the garage
- more stable
Ytong
- better thermal insulation
- easier to work with
Weak points are usually the windows, doors, gates... of course, you also have to insulate the roof. We put about 16 or 18 cm of insulation between the rafters.