The 2700 would have more power than the 700 and 800 series models. As you need double the power for a 3 dB change in SPL, and it almost certainly does not have double the power, it doesn't seem too significant.
The 2700 could have a better digital to audio stage, but as that's impossible to know and unlikely to be significant I think you can ignore it.
The 2700 supported DSD, which few people need. So you can probably ignore that to
Of course the 2700 was a better looking device, but what can we do Yamaha went blue, and to less pretty chassis. Matter of taste anyway
Not to surprised the 2700 is not fully operational. I replaced it with the 3900 then replaced that with the Z7 and my Z7 has some issues. I suppose nothing lasts forever but I expect a little better from these pricey units
I can't personally put faith in the Adventage line as I had an 820 fail after less than two years. Bad luck maybe. It won't stay turned on, and I can't be bothered to deal with getting it serviced so far. I suppose if I could get it fixed for under $200 it might be worth it, but what are the odds of that? Nonetheless Yamaha has mostly treated me well over the years. I am a mostly happy Yamaha owner.