The driver will run any motor up to its ratings, so long as it's not something cheap like the TB6560 which is generally over-rated. However that does not mean it's the best driver to run a 6 Amp motor, since a motor which requires that high current will be Nema 34 which benefit from a higher voltage supply. For the 3Nm motors you mention they are fine if you get them for a good price - maybe £100 for the 3.