I also believe the SVS-4 auto A/V switcher does the same thing.
I have not used the Vstab, but from the picture the switcher does more. The switcher has dial that ranges from 10:1 to 1:2. i.e. it can stabilize the sound or expand it (booms become louder and whispers fainter) while from the Vstab's picture it only has two settings 10:1, and 2:1
