Tritone substitution, according to the theory, is where you replace a dominant seventh chord (V7) with one a tritone away (♭II7). However, I believe it should not be a ♭II7 chord, but a ♭II(#6) chord. But these use the same keys, so how can we tell? Why not try just intonation, where ♭II7 and ♭II(#6) ARE different? In this project, there are three buttons. One plays V7-!. One plays ♭II7-I. One plays ♭II(#6) to I. All of these are in just intonation. Decide for yourself which of the ♭II choices works better, and post your answer in the comments. I would have used an ii chord ( ii7 - V7/♭II7/♭II(#6) - I ), but I couldn't figure out the tuning of the ii chord. https://en.wikipedia.org/wiki/Tritone_substitution