Can you turn it up so the sound is clear without distorting at 60 to 70 with the hood down?
Much as I like, and use, our sound system unless you want to supply music for the whole county I think you are asking a bit much for a sound system that you can really listen to at speeds in excess of 60. Under 60 is not a huge problem but over 60 the wind noise is likely to be just too much.
For reference we only have the standard system with the two front foot well speakers. I keep thinking it could be improved by placing two small speakers in the space just behind the doors. I don't want to lose even 1cm of luggage space to speaker boxes.