Ok, so I couldn't find anyone online who had done this fitment test. A lot of people have tried PSA uppers on Aero lowers - but I couldn't find anything vice-versa. This is a PSA gen 3 lower and an aero M5 upper (NOT the M5e1, although that only really impacts the handguard)
So I decided to give it a try myself, fully expecting it wouldn't work - and worse case scenario I build two guns instead of one.
Heads up before you read further - I haven't completed this build, so I can't tell you whether or not the thing shoots. This is just a discussion of the alignment between the Aero upper and PSA lower.
Which - it's hard to say. I did get them to mate in the end, but I had to file the edge of the take down pin a few thousandths to get there. Does that count as "fitting"? Probably not. Note too, there is a hairline gap at the back end of the upper where it contacts the lower receiver buffer tube area. Looking down the front of the upper, you can see there is a slight offset - the buffer tube is slightly below center.
I don't know if, or how badly this will impact cycling, but we'll see when I get there. Just thought it might be nice for those out there like me wondering "will it fit"? So far I'd say no, save your pennies and just get the right thing. But if you were like me and already had the PSA lower and didn't want to be stuck with their upper - well here you go. They technically will pair up, but you're going to have to ruin at least one takedown pin to get there, and it's not the prettiest thing at all.
Before anyone attacks me, yes, I know PSA states they don't play well with others, and honestly I didn't expect much. I don't recommend trying to get PSA to mate to other parts and pieces, this is just trying to add a bit more information out there that I couldn't find before.