Let's look at this logically. Is anyone here realy contemplating using a machinegun for home defense? What's the maximum number of home invaders that anyone has even heard of? Three? Maybe an outside chance of Four?
I'd say that if there were 4 home invaders, you could be logistically justified in using a full-auto weapon. But, anything less than that and you are simply better armed with a handgun, shotgun or some other kind of semi-auto gun.
Forget about the legal consequences for a moment - what I'm saying is that if I'm faced with 3 or less attackers, I'd be far more comfortable with a semi-auto. I'd be too concerned that I'd blow through my one magazine and not be able to locate another loaded mag quick enough! When I fire my AC556 - it "feels like" I've only got enough ammo for 2-3 bad guys. I'm sure that I'd have about 15-20 of those rounds damage walls, ceilings, floors, furniture, etc. It would be like using lighter fluid and a match to get rid of an ant infestation inside of your house!
Now, if we are talking suppressors - I guess you could always use it, take it off when your're done and toss it back in the safe or whatever. That wouldn't be too hard. Enough said on that.
As far as SBR's - if it wasn't for the difficulty of storing it when not in use, I'd say that would be a pretty good choice for inside your house. Large capacity, more accurate and more powerful than a handgun and easy to use.