I like the Micro-Restore type products , but they are not absolutely necessary. Products like the "free" (of dyes/perfumes) liquid versions of All or Purex are value priced and do a good job on clothing, linens and microfiber alike.
For extra dirty towels, a pre-soak or stain pre-treatment may help with the appearance.
1/4 - 1 cup of 5% white vinegar in the rinse water and you should be on your way.