You can use almost anything, it just depends on the degree of coarse or fine abrasion, and the level of polishing required. As an example I use the el-cheapo 20kg $6 bags of small crushed stones from the builders section in Bunnings, and use it dry for rough to medium sanding of steel parts. Does a mighty fine job too! And a damn sight cheaper than the equivalent roughing grits from the "specialty suppliers". Here in OZ every store is a "specialty supplier" due to the way we get reamed on products and pricing.
I did try the $6 bags of builders sand for finer finishing also but it was fairly slow going, and I was too impatient too wait and see!
Just try it and see would be my advice as it's basically only a sliding ratio between time, density, and parts. Aluminium oxide and steel ball bearings are a couple of very commonly used media for vibratory tumblers so I would think you'd be fine.
cheers,
Ian
It's rumoured that everytime someone buys a TB6560 based board, an engineer cries!