If he uses bass-limited speakers he can avoid some of the problems of having a square room though. A 15x15x8 box would have peaks at 75 and 150Hz at normal listening position with the coresponding nulls. Because even the best small speakers do not have the surface area or box cappacity to produce these frequencies at high volume levels he may have better luck with smaller speakers. I like the Spendors for just this application. THey give you a great sense of the bass that should be there because they roll off gradually.
Good luck!
Good luck!