Hi,
Sorry, I don’t know Roland TR-08s, but from the quick look, it doesn’t seem it can act as an Audio Device. So you can’t hear an Audio Loops from Cubase over TR-08s.
Use Focusrite 2i2 as your Audio Device and connect audio jack cables from Roland’s outputs to Focusrite inputs. Then add a monitor Audio track in Cubase. I.e. add an Audio track, set the input to the inputs where did you connect your Roland to and enable Monitor button on the track (to make sure the input signal goes thru Cubase engine to the output).