I spent a little time with the two on-ear pairs, the ES-FC300 ($149) and ES-HF300 ($179). The difference between the two is the cord -- the FC300 has a tangle-resistant flat cable while the more expensive HF300 features an "audiophile-grade" 6N copper cable.
I liked the understated look of the headphones and found them pretty comfortable to wear. They're fairly lightweight but don't feel cheap and have aluminum on the earcups (Onkyo refers to them as the aluminum driver housing). Both models will be available in black, white, and purple when they ship in March.
As for sound, it's what you'd expect from a more audiophile-oriented headphone: natural, balanced sound with good detail.
I wasn't able to test whether the HF300 model's 6N copper cable improved sound quality, but I did appreciate that both models have a special MMCX connector that's designed to disconnect under stress.
While neither pair of headphones offers an integrated remote with microphone for cell phone calls, Onkyo reps said it was possible that the company would make a remote/microphone cable accessory in the future because the cord is detachable.
In all, it seems like a good start for Onkyo in the headphone market. As I said, I didn't get a chance try the in-ear models, but they, too, are differentiated by their cords, with the IE-FC300 headphones priced at $129 and the IE-HF300 headphones at $99. The in-ear models should also be available in March.