I think the sound you are hearing is simply due to the coarse texture of the grass. St Augustine has a wide leaf blade and large stolon compared to many lawn grasses. St. Augustine should be mowed at 2 1/2" in sun and 3" in the shade. If you are not mowing at the proper height try doing that and see if it helps. I'm not familiar with dillo dirt but additions of compost or peat moss type products are helpful on St Augustine. Their low ph helps keep take all patch out of the lawn. In regard to seeding another grass: I think that is a bad idea. Mixing lawn grasses is not a good strategy. Different grass species need to be mowed at different heights, fertilization timing and rate is often different. If you can't get past the texture and want another grass you would need to remove the St Augustine and either re-sod or re-seed another species of grass. Which species would depend on location, shade, soil, etc.

Patty Cakes,
In my experience, if walking on St. Augustine sounds like walking on plastic bags all the time, then your lawn needs some watering and fertilizing.

See the link below for St. Augustine care. This is the FAQ page for organic lawn care, but even if you chose to use non-organic approach, the general care guidelines still apply.

With regards to Dillodirt, do a google search for it and read up on how it's made. You tell me if you want to walk around in bare feet in that stuff. It's chemical and hard metal city. I remember a few years ago when the City of Austin decided to spread dillodirt around at Zilker Park right before ACL, or one of those events. It rained, and so people were walking, dancing, rolling, playing in the "mud", and their skin reacted to it. Some had burning skin (like a chemical burn), while others had general redness. No way- not for me! But, like txtreegrower said, spreading compost is beneficial for the lawn. It is a good way to get beneficial microbes into your soil if your soil is in bad shape.

Here is a link that might be useful: Garden Web Organic Lawn Care FAQ