Max,
The only user I can recall using a 16803 for sure is @jbalsam (maybe @mstriebeck?). Haven’t either around for a bit…
Hi-speed mode is only used for frame and focus and plate solving (so yes on the centering question). Can you post logs? How many speeds does your camera supports (how many are in the drop down)?
Here is a post where he indicates both modes seem to be working.