A home cinema is very rarely playing at reference volume. Reference volume is what they use in the Cinema, and is very loud. If your volume is lower than what the mixer made at reference volume (his volume level in the mixing room) then it sounds different. This is because human hearing is not entirely logharithmic. This means that if you play lower than mixing volume, the bass will sound lower. In the old days they tried to compensate for this with a loudness button that would boost the bass. But that would be a fixed amount, and not correct at every volume level.