i have a duet wifi which supports 2 z motor connections in series native to the board. Sadly, i have been an EE for over 20 years andclearly have forgotten much as i should have known better. IMHO, series is the way to go for stepper motors not parallel. This was posted by a much smarter man than me in the duet wifi forum and is a good breakdown. i also wired my y stepper motors to the same driver (just married wires in connector) this was a lack of knowledge on my part. Since i only have 1 extruder, i have a spare port free for a 2nd extruder motor drive. In the software you can specify what ports serve what axis so ideally i should have put 2nd y motor on E1 then modified software so 1 is driven backwards and 1 forwards. Again, this is for DUET WIFI so if you are using another board this may not apply to your system Quote from David below.
When you connect multiple motors in series, the available voltage to
each reduces. This doesn't normally affect the static torque available,
because the motors we choose for 3D printers normally need only 3V at
their maximum current [except that there are some motors available rated
at 0.4A 12V - avoid them]. However, the faster a motor moves, the more
voltage it needs because of inductance and back emf. So when you connect
motors in series, you reduce the maximum speed you can run them at
before the torque starts dropping off. See https://duet3d.com/wiki/Choosing_steppe … e_you_need for how to estimate this.Z
axis speed on a Cartesian or CoreXY printer isn't normally critical, so
connecting motors in series works well. If you do need higher speeds,
use 24V power instead of 12V.