I have used the single axis TB6560 drives that you have and have not had any big problems ever. Most of the problems you hear about are the all-in-one boards that have 3 or 4 zxis drives built in and a integrated BOB as well. I think the drives you have will get you going.
Having said the above, the single axis TB6600 drives are better. I have some of those too and the cost isn't any higher than the TB6600. So, if you do blow one of the TB6560's then I would replace with a TB6600. The ones I have look a lot like the TB6560's you have with an exposed circuit board. I think the last 3 I bought cost $18 for 3 of them. They work well and theyseem smooth. They do have a couple problems as bought and won't produce the full 4 amps, but if you don't need it they work great. It is also fairly easy to fix them if you need to. Here is a link to the ones I have and a little bit about them.
http://www.cnczone.com/forums/steppe...ml#post1979892