Thank you a lot for your response. Really appreciate it!

Really?! From who/where?

I should clarify that I didn't mean they were bad period, they are bad COMPARED to the dr-680mkii. I've heard this about 40-50 times, 30-40 from people online, and five people I know and trust quite a bit in real life. I have also used the H series quite a bit, and now own the dr-100mkiii which sounds WAYYYYYYYYYYY better (to my ears), so I wasn't surprised to hear that.

unless they believe the F8 sounds bad too....

they do say the F8 sounds worse than the tascam, but that both the f4 and f8 still sound great. Sorry if the way I wrote it was confusing.

You see a few naysayers, but I'd just call them luddites

Luddites were people against technology/preferred manual labor to machinery. These 'naysayers' just prefer different technology, so that doesn't make any sense at all.

The core functionality of the DR680mk1 and mk2 remain basically almost the same

Dunno what you mean by core functionality. I'm sure most things are the same, but the pre's have a new op-amp and capacitor, which I've been told has significantly improved the sound quality. I've heard this about 40-50 times, and you are the FIRST person I've EVER heard say otherwise. So I dunno. I still reserve judgment until I can hear the difference myself.

so it is not just that the Zoom F series sounds better

That is really the first time I've heard that. Have you used both? I truly do value your opinion, and would like to hear how exactly the F series is better. Better s/n ratio? More warmth? Despite the sound quality, I was leaning towards the F8n for my interim deck, until a 688.

but also that they're capable of so much more

what more are they capable of? I mean, I know a few differences where the F series does better, but I'd like to hear it from you.

Again, appreciate the differing opinion!