Bill, not sure what you mean by a lot of the buttons do nothing; they're all assigned to something (but usually context sensitive); your salesperson should be able to give a walkthrough of how to use it; if not, there are a ton of tutorials online.
However it seems it's the sound that disappoints you; do you mean through the speakers? Or headphones? Because the DGX670 sounds considerably better through headphones; the speakers actually crackle at full volume when playing the keys hard, which is *not* good.
Biggles: you can love Korg and hate Yamaha, absolutely your choice. However, I think what the OP is asking is for other board suggestions (not even how to use his). Bill: you didn't find it intuitive, and again, that's fair. I can tell you we've sold many, and the only customer complaint I had? One regular customer, I warned him that the speakers crackle at full volume, so play at 70% or use headphones.
He came back a week later and said "Man, I thought you meant just your display; but you did say the model. I wasn't expecting mine to crackle at home, but it did too!" The reason he thought I was kidding? All the previous models, I can crank them full, play piano keys hard, no crackle. It's just the 670.
Are there alternatives? I'm going to compare using $CAD list prices; the DGX670 sells for $1199 in Canada. Is there anything else I'd have recommended?
Yes, the PS500 (originally nearly double the DGX at $2099) is a nearly perfect piano with arranger functions; 40w speakers (instead of 12), no frap or crackle at full volume; the piano sample is considerably better than the DGX (indeed, it sounds better than the Genos piano... it's the same piano as the CVP705, CSP150/170), and uses your phone or tablet to navigate (so, incredibly easy to Navigate). And at Christmas, Yamaha Canada put them on blow out for *less* than the DGX. So to me, no brainer. *BUT* you can't make or import your own styles onto it (yet).
Now, there are a couple of other alternatives:
Roland FPE50: slightly more compact, and *much* better speakers than the DGX (not quite as good as the PS500, but the Roland's 22W speaker *does* have even more bass punch). The Pop/HipHop/Dance/Trance beats are great, since both the bass and drums have a real beefiness to them. $1399 selling in Canada. It's also slimmer and ligher than the DGX, and I think easier to navigate but a *lot* fewer functions.
The downsides: modelled piano never sounds as real as a real sample, so it ends up sounding a little hollow (as posted on here elsewhere); Additionally, the acoustic guitars sound sad compared to the DGX (classical and acoustic) so most of the styles avoid strumming (wise decision). And there's no scoring feature like on the DGX (music notation). And no way to make your own styles, or read styles from a USB stick like the DGX (there are literally tens of thousands of Yamaha styles available). However, Roland does have an OS update that adds about 40 new styles; so new styles are at least possible; you just create your own like on the DGX. (The PS500 also has no style creation)
Korg used to have the Havian 30, and for $2099, this was also excellent. Touch screen navigation, *great* sounding styles and piano sound. Too bad they discontinued it. No the piano and accompaniment wasn't as good as the PS500, and even the touchscreen interface wasn't *quite* as intuitive, but the Havian 30 launched in 2015, the PS500 had the tech advantage simply launching 8 years later)
The PA5x88 is an alternative, sure, but at $7499 CAD it's not even remotely similar a pricepoint to the DGX @ $1199 (which *many* people have purchased and enjoyed, and indeed, one of the youtube channels, can't remember Leigh or Woody, says that's what he'd get over the PA5x or Genos 2

). The DGX is the absolute bang for the buck 88 key arranger model (except in Canada, where the PS500 was the clear winner, but now sold out and discontinued), but the DGX certainly has limitations.
But it *is* cool to stream music in, play and sing along with that music, and record both to your usb stick, with only a couple of button presses.
But even there; the ps500? 1 "button" (touchscreen on screen button) press. As simple as it gets.
Mark