Hi @Neal1,
The first constraint is the mount diameter, as the 80mm mount is not compatible with the Z-plus, so you need to shop in the “65mm spindles” alley. I’m not sure 65mm 2.2kW spindles exist (but I did not look for them either), so that would steer the decision towards a 1.5kW or 800W spindle. Which are also significantly lighter than the 2.2kW monsters (I have one…), so this will help the Z-plus as it won’t have to move 10lbs up and down with its ballscrew.
What are you cutting? I know the appeal of “more power” is strong (guilty as charged, I really didn’t need a 2.2kW spindle myself), but if I had to fit a spindle on a Z-plus myself today, I would probably consider an 800W water-cooled model: they’re not too heavy, very quiet (the main reason I got a spindle), and you will have automatic RPM control (which I could not live without now). You will not get “more power”, but maxing out power on an 800W spindle already requires pretty aggressive cuts. This thread might be of interest:
Mounting a 1.5kW spindle on a Z-plus may work, but I guess you will be putting extra load on the leadscrew nut, so it may wear-out faster (which I guess is why support did not recommend it)
Just food for thought, actual Z-plus+Spindle owners may have better insights!