First of all, you want to plush up those fibers that have become matted and hard. You can do this by washing your luxury towels, a few at a time, with a small bit of laundry detergent, and then putting a cup full of white vinegar in the rinse cycle. The vinegar serves to loosen the fibers up in the soft towel, helping them to be restored to their original state. Also, the more times you use the vinegar in the rinse cycle, the softer your towels will become because you are slowly removing the chemical build-up that has occurred within, since you began washing them.
Never use too much laundry detergent, it reverses the cleaning affect that it is supposed to have and bogs your soft bath towels down with too much junk to be cleaned off effectively in one washer load.
Skip the liquid fabric softener and the dryer sheets. While they claim to make items soft and delicious smelling, what they can really do, especially after time, is build up residue on your thick towels that weighs them down. Fabric softener is good for reducing or eliminating static cling, but the adverse affects are a waxy build up that destroys the absorbency of your towels. Air dry your towels, if possible, and then put them in the dryer on the air fluff cycle for about fifteen minutes. You will be very surprised at how much of a difference this can make after just a couple of washings.
Throw four or five dryer balls in the electric dryer with your towels, if you have to use one to get them dry. Once they are dry, fluff them for a few minutes before folding. The balls serve to soften and fluff the towels, as well as remove any lumps.
Never put more than a few towels in an electric dryer at once. Towels are heavy, and too many of them will keep the dryer from working as it is intended to do. The longer it takes to dry the towels, the higher the chance they will come out scratchy.