I think you overestimate the effect each of those 3 have.
Yes, both benzos and alcohol can help potentiate most drugs like opioids and barbiturates, but they won't be as effective as taking a larger dose of said lethal drug. What I'm trying to say is they shouldn't be used to help make up for a lower dose, but rather to give a higher dose more chance of success.
Also sadly tramadol is an incredibly weak opioid, it's only 1/10th the strength of morphine, and morphine isn't a strong opioid to begin with. The 5-drug mix in the PPeH uses 15g of morphine, and that's in combination with 4 other drugs. So I imagine if you tried CTBing on morphine alone, you'd have to take more than 15g, say about 25g.
For any good chance of CTBing on tramadol I think you'd have to take 250g of it, and that's a lot.