Try adding some vinegar to the fabric softener dispenser, or just add to the final rinse. About a teaspoon per towel, I just eyeball it. It does wonders for softening up stiff towels. Folded my soft towels about an hour ago...
Dont worry, they wont smell of vinegar. Also consider using less detergent, what you describe sounds like too much was used. Although many say its not worth it I swear by Micro Restore detergent.
Try the vinegar and less detergent, two rinses, bet it helps.
Good luck
PS: also does wonders on your household towels...