No way to know what is in there but I suspect it is DW1 or maxlife (the two most popular choices). Also the universal ATF can be mixed in any proportion with DW1 so you may even have multiple brands.
Personally, I prefer Maxlife over DW1. I would do a single drain/fill now, and drive normally throughout the week. Then repeat each week until three or four drain/fills...that should be sufficient to remove the particles you mentioned in the first post.
On a related note, if you are not the original owner it may be worth evaluating the power steering and brake fluids.
