The analog outputs on the 7356 only work fine for motion control applications in closed loop mode. So in your case I recommend using two 7334 boards for the steppers and an analog output board for the piezos. If you need hardware timed analog output (e. g. to output a defined velocity profile), the PCI-6733 is a good option. If software timing is sufficient, you could use a board like the PCI-6703.
Jochen
