A benzo will definitely dull the trip, however, I have taken 10mg of valium before and during trips on mushrooms, 2C-E, and 2C-I. I tripped every time, with very little anxiety, enjoyed, but every time always leaves me wondering how much
harder I would've tripped sans-benzo.
Opiates + shrooms I am absolutely DYING to try. I want to try a nice stimulating dose of kratom plus some shrooms. The stimulation will help with the sleepy-shroom-onset, and the mild euphoria will diminish the anxiety almost completely. Of course, I would be smoking weed too, but I wouldn't start with the weed until I was well into the trip. I would look at it as a kind of organic ecstasy.
If taking shrooms and kratom (or any opiate, pod tea sounds lovely) feels as I expect it to, basically just the way both drugs normally feel except at the same time, then I will probably do this over rolling any day. Any time I take kratom I long for visuals, and any time I take a psych I long for some kind of pushed euphoria, but just enough to send my mind in the right direction, then I'll let the psych take care of the rest. Taking shady synths kinda sucks and I feel like MDMA is an amazing but empty high. Something that produces a feeling that many would argue blows MDMA away AND is 100% organic, from the magical earth AND proven perfectly safe....yeah I'll take the latter kthx.
Ok I'm rambling sorry, I'm not trying to hijack the thread. To answer the question short, yes a benzo will dull your trip but you will still trip (tolerance depending of course). I have no idea how opiates would effect your trip but I'd imagine it is along the same lines, but probably better to take than a benzo. I feel benzos are meant to take you out of that kind of crazy mindset and make you not care, however, I sometimes find opiates can induce their own moderately introspective mindset.
Hope it helps.