Hi Pab, welcome to the forum. I will be using Rutex drivers and servo motors for my cnc and I too have in mind to work with 3 axis and switch over to 5 axis. The thing is that the type of driver cards that I have only accept servo motors only which are a bit expensive compaired to stepper motors, but I beleave that Rutex have developed driver cards that accept steppers as well, the only thing is that their mother board only handles 4axis but one could have 2 mother bords and and 5 driver cards. You will then end up with 2 printer ports to connect the driver cards and naturally have to add another 1 or 2 to your PC. Their address is http://www.rutex.com and the only affordable software I have found that could handle 5 axis is Mach 2 and if not mistaken has the ability to conigure the printer ports, inwhich case will be using 2 for 5 axis. I'm not quite sure if this is the kind of setup that you want, however always consult with the suppliers to guide you through as I too am new in this field. As regard to other CAM software I guess one has to pay a good amount of money in order to handle 5 axis.
I hope I have been of any help.