Listening to "people" is usually poison, one shouldn't do too much of it. Is the machine doing what you expect? Are you happy with it? Do you now have the flexibility to do things you haven't imagined you would, but now are capable of? If you were only ever going to play live, you may have overbought, but now consider what possibilities now exist. Someone else can line-by-line enumerate the deltas. The AX-8 is cheaper, yes, and it does many of the same things, however its flexibility is reduced in subtle ways in many functionality areas to meet the goal of that lower price. Overall, that answer to the original question is no, it cannot replace all the things an AX-FX XL+ does.
Buyers remorse over price is one thing, but externally induced buyer's remorse is just silly.
Furthermore, posts in "various forums" is the worst place to get information with which to make decisions. Bear in mind that most forums attract a certain kind of personality, the kind that loves to pick apart every little detail, dirty it up with their own slant, start arguments over the merits of infinitely stupid nitnoid crapola, troll, find ways to insidiously push their agenda, and so on. They do this for any number of reasons; they have too much time on their hands, they're insufferably boorish in the outside world and no one they are around wants to have a conversation with them, they live in their parents basement as they dream of being things they'll never be because they are unmotivated to do anything more than go to their crap job at the Quik-E-Mart and come home to spout off on all the BS they concocted in their heads as they were flipping burgers.
That's my one long post of the day. Me scusi per favore, I have a fellowship grant proposal to write. Ciao.