^Combos are definitely my favorite, especially with psychedelics. I don't enjoy benzos or alcohol much on their own either though (I used to, tolerance be damned). I find that trips on multiple psychedelics are always better then trips on one psychedelic.
Yeah, opiates still decrease the strength of trips, but not nearly as much as GABAergics. What opiate are you doing? My favorite opiates to do in combination with psychedelics are probably heroin and opium (or pod tea or whatever), because I find heroin and opium to both have a trippy quality. Codeine mixes great with psychedelics too, I've never tried oxy with them but I can't imagine it being bad.
One thing though is that I think it's best to dose higher on the psychedelics and only a medium dose of an opiate, if you're trying to obtain ego death. Mushrooms + LSD + opiate of your choice + DMT or mescaline (or both) would probably work well. I've never done this, but I'd like to combine an opiate with DMT in a shot.
Opiates are a go, but not at high doses (aim for them to not be the primary thing if you want ego death). I would combine them with LSD and at least one other psychedelic, if you can. DMT is good at helping with ego death, or causing it all on its own. Dissassociatives can help vastly with ego death, but I don't recommend pcp for it. Ketamine and DXM are good though. DXM, LSD and mushrooms is one of my all time favorite combos.