I realize this is a very old thread, but I had to chime in regardless.
If you're solidly on a standard maintenance dose of suboxone, let's say 8mgs daily, for any length of time, no normal amount of H will get you high. The danger comes when you decide to shoot 3x your normal H dose to "break through". You may feel slightly high, but a majority of the H that binds will be binding to receptors that aren't in your brain, ie in your bowls and spinal cord. CNS depression is in fact happening, but no euphoria. Thus the OD potential. It is not, however, a cumulative effect of both Subs and H. It is merely the large amount of H you just took. This is why, IMO, that trying to break through a maintenance dose of subs not only a waste of $, but if done with enough gusto, could prove fatal.