I have not seen anything in the way of drop dead instant gratification/difference to comment about.. sleeker, yes, more i/o, yes, more horsepower, yes, more routing, yes.. fundamentally better?.. jury is out...honestly?..if someone was to give me $2k i would sell it in a heartbeat the ax8 offers the entire footswitch bed, with mode switches for patches, scenes and pedals so is highly useful straight out of the box.. and the fm3 has 3 buttons and so you will definitely need (at least) the FC6, and probably the fc12 ..so thats more like $1700 for fm3 and equivalent footswitches...making the $900 a bargain..lol
Don't worry about updates, if you like the way it sounds and works... Don't kick sleeping dogs! They should call them "down-dates" because every time I'v so-called updated something, I later wished I had not. If something works good, is rock solid, why in the world mess with it. People always think they are missing out on something if they don't have the latest greatest, and it latest might not be the greatest.
No, you will not "definitely need (at least)" an FC6. I can totally understand if you want that, but its not required in any way, shape or form.
I have a Helix I watched comparison vids for the AXE & Helix endlessly. In blind comparisons, I almost always prefer the Helix for some reason. I wound up with a Helix Rack & foot controller. I use it 4CM with my 40C & also use the Helix as my interface. The Helix interface sound quality makes the Focusrite sound like a toy to my ears. Since I've learned more tricks, I rarely use the 40C pre-amp & run the Helix amps & preamps into the FX return. I just ordered a Powercab for the Helix to test for low volume playing.
The powercab is cool—that plus monitors makes for a great, immersive low volume solution. The AXE is great too—tbh I was turned off by the proprietary IR formats, and the UI was basically useless for someone with bad eyes. The rack/midi floorboard combo is a big fat chunk of change too. It sounds great, but I couldn’t discern one from the other after gigging with both dozens of times. Half the price and I can throw it on my Sweetwater card? Done.