Soffit mounting is used in studios so that the window into the studio is left unobstructed. Better than soffit mounting is in-wall mounting either side of a window, but that is often a problem with space and/or size of the window. Whether soffit mounted or in-wall mounted, the techniques are the same, and would indeed suit home HiFi if building a dedicated listening room. It's pretty much impossible to do this with 'normal' home building methods, whether dry-wall or solid wall.
One very sensible and very close alternative to in-wall mounting is corner mounting where a triangular enclosure is fitted very close to, but not touching the walls, with the gap filled with a compliant material like silicone rubber or foam. The main problem in most houses is the absence of suitable corners, but again, if it's a new build music room then it's quite possible. I almost did it myself, but decided to move to another room in the house, so glad I didn't.
For lots of technical detail, have a read of Philip Newell's book, Recording Studio Design.
S.