Correct me if I’m wrong but I guess you are talking about the input of your Digitone right? Before testing I would have said 100. and unity gain as in input = output?
So I just tested this with my ST.
I connected the inputs and outputs of my ST with balanced cables. Using Overbridge, I set the input & output device of my DAW to be the ST. I let a loop (or any audio material for that matter) play. I inserted a vu meter, then external device (input 1&2 & output 1&2), then again a vu meter on to that channel. The vu meters matches at 103 (the value of my input on the ST).
Why not exactly 100 could have sth to do with the filter of the AD DA converters, the cables, overbridge or some setting I missed on the ST.
Test it yourself but I would say somewhere around a 100 should do the trick.