Minimizing wall thickness for basement drywall?
When the construction is non-structural, then 1x furring strips can be used to attach the gypsum board. However, for a home theater, prioritizing acoustical performance may make more sense than prioritizing an inch or two of additional floor area - particularly given that furniture/equipment selection and arrangement is more directly related functional floor area.

This is to say that selection of construction systems that minimize the transmission of airborne and structural sound may be worth more than going from 14'-8" to 14'-10" in room width. What matters is how the space is allocated to provide better function.