I looked at the manual this time and it appears they are AC servo drives, they use the hall effect commutation pulses to start up and then use the encoder for commutation, so you need to look for a AC or DCBL motor that has encoder and the 3 Hall effect outputs which now a days has them simulated on the encoder disk, so you also need a motor with encoder with these features.
When looking for a motor, beware that many AC motors have resolver, which cannot be used with these drives.
I look for Tamagawa, or Applied Motion, which are the same motors, also good, Aerotech, DMC, & Reliance, which are now owned by Allen-Bradley.
And it also depends on what torque range you need.
There are many Yaskawa motors, which are supposed to be excellent but I have never personally used these.
I would get the 60v versions as the drive is 80vdc max and they also state to not used any supply that is more than 5v of the rated motor voltage.
Nosmo