I'm going to make a prediction here: You will be back in a few months or weeks or days telling us how the TB6560 driver suddenly stopped working one day. First, it's not designed for higher voltages, as H500 indicated the power up sequence has to be changed to get logic power first, which is difficult to do reliably. Second, spending $100 to downgrade the motors to keep the same driver is backwards. Instead use that $100 to upgrade the drivers. If you can't afford a geckodrive, save some money by buying and building a kit. Not only will you have a better driver than the TB6560, for less money, you will also know how to FIX that driver if you have problems with it in the future. Obviously, I recommend my drivers, which would be under $100 for three and will give you 4 amps at 50 volts or 200 watt capacity. More than enough for those motors to work well... want proof? Here's a local user of my drivers who upgraded his chinese kit:

I'm not saying this to be mean or to bully anyone... you do what you think it right and I'll support your decision. I'm saying this because I've seen it so many times before. TB6560 drivers are NOT intended for this use, they eventually die, and good drivers at the right voltage make all the difference.