So I returned the Onkyo as the yamaha had better sound after the ypao. I couldn't get the Onkyo to sound good. I'm considering the 2400 as the upgrade to the 3400 seems not to be significant enough. If I were to get the 3400, would the yamaha rxv685 be better or should I stick to the Denon?
I can assure yo the 3400 will sound good as it really has no sound signature. I found that out when I compared it side by side with my much higher end separates.. The RX-V685 should be transparent too if used well below it's power output limit. I am talking about pure direct mode, if you engage DSP functions including Audyssey, then it all depends.. In that sense, I would say bite the bullet and go with the 3400. As HD alluded to, XT works, but XT32 is much better. If you are of the OCD type like me, who not only want the bass to sound good but also look good, then you should bite another bullet ($20) and get the Audyssey Editor App.
It seems like you prefer smooth and not exaggerated bass, if that is the case, more reason to get the 3400 and before you run Audyssey, read the instructions careful, then follow it to the letter, and re-adjust the crossover points manually after. If you wouldn't mind exaggerated bass, Audyssey may disappoint you, but then you can always tweak it manually to your taste, there are more flexibility than just on/off, than a lot of people think.