I bought the us4 over the 4 pro only because my budget was already stretched going with the 4.
if i had my time again i might have gone the 4 pro but i am happy with the 4
here’s the differences
https://www.head-fi.org/threads/nii...s-by-lake-people.876018/page-54#post-16504828
for me (again) the niimbus is great with susvaras and i have no need for any other solid state amp but probably a bit of overkill if you are needing that much power.
at the end of the day me buying the susvaras and niimbus was pure indulgence because i was lucky enough to be in a position to buy them a couple of years ago. And i have not heard anything better that has caused me to change my set up.
But we have hit the point of diminishing returns as we approach the susvaras and relative amps - hence why i find it an indulgence and (luckily) my only one
and as I keep saying - this hobby is all subjective
ps i find the susvaras to have a great openness/airiness in the upper end ()not excessively) that i really enjoy