I use one tower and one sub. I borrowed a second sub from HankB and I could tell no difference in sound at the level I was playing. I'm certain that at really high levels the second sub would make a difference.
I plugged and unplugged it during the evening and no one could tell any difference in the sound, including me.
As for service, I did have a problem about 13 months after I purchased the Bose. It started making a loud crackling noise. I was able to reboot it and make it stop.
I phoned Bose the next morning, a Wednesday. They had me do a test or two, then overnighted a new L1 unit to me. I had it Thursday morning. I then returned the old unit to them. That was it. Great service. I've had no other problems at all.
DonM