I ran across a friend who's a fellow audiophile who advised me that after my newborn son arrives in 3 months time that if I plan on getting serious speakers with a decent sub I should consider that I won't be able to run my system volume at pre-baby levels without waking up the child.
I find this information false. Our first addition to the family was a set of twin boys and we always played music and many times they wouldnt go to sleep unless we turned it on. I cant tell you how many times I have heard Eric Claptons' 'You Look Wonderful Tonight'.
When a new family arrives, its best to carry on with business as usual as then the baby get familiar with the noises that go on during the day. To many people these days try and be all to quiet when the baby is sleeping and then the slightest little noise ends up waking them up.
My kids to this day ( the boys are 16 and our daughter is 15) can sleep through the music at whatever level I have it at as they say it relaxes them.