Hi Kacki,
You ask if Roon’s room correction will offset the potential loss of your 518. Personally, I don’t think Roon is good value simply for room-correction alone. When you take into account you don’t listen much to your ripped music collection now you have Tidal, there’s little else Roon can offer over the T8. You’d be better off putting a drive into the T8 and moving your music files to that and playing them from there rather than Roon.
Also, don’t expect a magic bullet with Roon’s room-correction. It could make a difference, but it could also be a massive time-suck trying to get a satisfactory result. It would be more effective, and visually pleasing, to add or re-arrange furniture in your room before you go down the route of digital room-correction. After all, you want to spend your time listening to music, not fiddling with EQ slopes.
And finally, don’t get too hung up on 24/96 vs 24/48. You don’t mention what music you listen to, but with most pop and rock music, it’s debatable that 24/96 will make much of a difference compared to CD-quality 16/44. If it’s jazz or classical then you may, possibly, perhaps, notice some improvement (we all hear things differently). It’s important to note that the way the music is mastered will make much more of an impact than different sample rates.
Whatever decision you take, enjoy the experiment and, most importantly, keep enjoying your music. And let us know the final result!