So, I want to preface this in saying that I've never had a comedown from even super absurd doses of MDMA, MDA, 5-MAPB, or 6-APB. I also am a well known dosedemon who can body very dangerous doses of most drugs, I suspect due to accumulated brain damage and 3 (almost 4) missing organs at this point.
I have combined 6-APB and MDMA, the batch of 6-APB I had was fully active at ~65mg and 90mg was exceptionally challenging, to the point that I would consider it to be edging up on a medically serious overdose. Benzofurans (though ESPECIALLY 6-APB) have a proclivity to have dosing variances between batches for a variety of chemistry reasons I could articulate if you're interested in them, but I'll leave the nerd shit out for now. My normal dose of MDMA is also ~175mg as I'm something like 100kg. When I mixed 6-APB with MDMA, I first did 25:75, then a few weeks later 50:125, then a few weeks later 70:150 (all of those ratios are structured as 6-APB:MDMA) I found the combination made the hyperthermia exceptionally overwhelming, and the euphoria didn't increase, but I would roll for no less than 16 hours on any of these experiences. It honestly got to the point where I would get sick of rolling, once you break about 12 hours it starts to become a little bit annoying.
It's also worth mentioning that this combination was consistently so intensely visual, it reminded me of the time that I (incredibly foolishly) combined 25C-NBOMe with MDA. 6-APB is kind of like a turbocharged, longlasting, hyperthermic, super visual variant of MDA, and it acts accordingly when mixed with MDMA.