You probably need less than you think you do for Roon, unless you have a really large library. Certainly the 8i7 is plenty (that’s what I use).
In the thread above we compared @simon_pepper’s i3 against my i7 for everyday stuff. There was nothing my i7 could do that couldn’t be done on the i3.
Note: single core clock speed trumps multiple core capabilities. The i9 would be helpful if you were doing a single box Roon/HQPlayer install (using SGC’s OS). But otherwise it’s just a bunch of wasted cores.