I'd recommend taking the 6-APB first and then the MDMA as others have stated, due to 6-APB having a longer duration and also taking a lot longer to reach peak (2-3 hours usually, vs the 40-90 minutes with MDMA).
I don't find that 6-APB feels all that psychedelic except at higher doses but there's certainly a touch of it, and at higher doses the visuals can go from almost non existent to pretty strong - during my latest experience the haloes and trails were unreal, I could barely see!
^ Just a note that the doses talked about in the above post are incredibly excessive - the most I've taken in a session was 250mg and it was definitely far too excessive and not something I'd repeat, the side effects greatly outweighed the pleasurable effects at this dose and I had a very unpleasant week long hangover (while I normally don't get much of a hangover at all other than feeling tired for a day or so with this) - most people seem to find it great at around 125mg or so, but personally I've always preferred around 150-170mg.
I've noticed though some of my more powerful experiences were actually at oddly lower doses, one of my strongest rolls to date was with just 80mg - however I did add a little amphetamine throughout the night so that was likely to blame.
I'd advise you try 6-APB on its own before combining the two, as I know for example the 6-APB + 5-APB combination is so damned good that had I tried it first before 6-APB on its own I don't think I'd have ever found 6-APB on its own quite as magical as I do
Regarding dosage, I'd go far lower than a usual dose of both when using them in combination, something like 60-70mg MDMA + 80-90mg of 6-APB maybe