As the T8 has Tidal built in already and that’s your main source of music I would just link the T8 direct to the 5500’s. It’s not a cheap unit so it should be a good performer.
Keep the system as simple as possible.

You could use Roon and fiddle around with various settings but it is likely to offer little over the native Tidal in the T8. In fact it could open you up to more tweaking and problem solving than you might want.

The 518 will be doing something in your chain and you understandably have gotten to like that a lot. So, when making any change, give it a lot of time to let your ears/brain acclimatise to the presentation.

No harm playing with various combinations though
E.g. 518 in, 518 out, Roon to T8, T8 direct to DSP

But for me I would go super simple with T8 + 5500 only.

Rgds,
Nick