To the original poster: given access to in-room measurement and PEQ, the box's qtc only really matters in the context of driver choice, box size, available power, and desired output SPL and bandwidth, and is not directly applicable to final sound quality. What you actually hear at your seat is the combination (well, technically, convolution...) of system and room responses.
In short, don't worry about the "sound" of a particular box qtc. Build the box according to your application constraints, measure it in the actual position in the actual listening room at the actual listening position(s), and move and/or (parametric) eq accordingly. Because that's what you finally hear. Qtc is a useful measure, but not nearly as useful as many would have you believe.