There is no way I could ever listed at full volume, and I'm confident the sound would continue to be clear as day.
Adding the subs definitely fills in a hole at the low end. Once you add them I think you will be extremely satisfied.
Glad to hear things are moving along. I soldered up some more patch cables to get the buttkickers completed around 8pm. I sat down to test them, popped in Avatar to the pillar scene. Test completed about 9pm when the movie was over Even my wife came down and watched when she felt the rumble of the subs.
Like you, it's nice to have some support in the family and even nicer when they too enjoy it.