YES.
I couldn't say the same for picamilon, (haven't used it), but I've personally found a combo of phenibut and diazepam, among other benzo's to be the most addictive and euphoric "downer" drug combo I've used. Course, people have mixed reactions to phenibut, so this won't be true for everybody, but phenibut is a mild euphoriant for me, as well as an anxylotic, so adding a benzo to the mix is very moreish to me, so I'm finding it quite difficult in keeping the 2 separate.
I wouldn't call it a potentiator, but it's a very effective synergizer IMHO. I've no experience with Tagamet so I really couldn't answer that one.
Edit: I should also add that I take 12 mg of suboxone daily.