For example, the sound of a rifle shot travels at the
velocity of sound in air and its velocity is independent of the velocity
of the
rifle

Yes. However, if you are travelling in a car at a velocity relative to the
air, the velocity of sound will be different for you than for someone
stationary relative to the air. On the other hand, if the car windows
are closed, the car is carrying a pocket of air with it, and the sound
will travel again at the original velocity inside the car.

Similarly, if all moving frames were to be dragging an 'aether-space'
along with them, the velocity of light could be constant in all frames
and light could function in the aether similarly to sound in the air.

Thus, I think that SR need not specify the non-existence of an aether.

Alen