Yea I'm researching that right now. The Centroid requires a minimum of at least 1000 ppr encoders and recommends 2000ppr/8000cpr encoders. Trying to find documentation on the Gecko to see if it supports that.
I will look into those brands shortly. They may very well be tach feedback. From what I have read/seen, replacing the old resolver/encoder and leaving the tach in place but not hooked up should be ok?