Do you think he would need all that for music only listening?
IMO, serious music listening is a lot more demanding, high-fidelity wise, than the acoustic precision required for watching movies.
Using only one sub is not an ideal situation if one wants to benefit from a more balanced frequency rendition. It is easier to obtain a smoother response by using two or even more subwoofers, depending on the size of the listening room. An important factor in the decision to go for multiple subs is the type of music and the lowest frequencies to be reproduced. For instance, if the audiophile likes to listen to pipe organ and electronic keyboard, he will benefit from having adequate subwoofing.
Classical organ, symphonic, choral and operatic music can demand dynamic peaks in excess of 30db. Amplifier power with adequate headroom driving one or several subwoofers is recommended, more so if the main speakers are not designed to handle the power required and cannot reproduce the input subwoofer frequencies.
Of course, finally the type of required equipment depends on other factors such as the listening distance from the speakers, the peak SPL levels aimed, the spouse acceptance factor etc.
