I just want to throw out a quick HF-2 comparison with my RS-1, which is about 6 years old. They are both amped by the rig in my signature. I like the rs-1 far more than the hf-2 after about a week. I find the HF-2 too undefined in the low end for me to really love them. The hf-2 bass is uncontrolled and tends to overwhelm some of the music for me, especially acoustic guitar. The rs-1 by comparison has much tighter, punchier, and more tuneful bass than the HF-2. I haven't ruled burn in as a possible solution to this problem, but my HF-2s already have 150 hrs on them, and I don't really believe in burn in to begin with, but I guess I'll have to wait and see.
The soundstage and presentation are also different on the HF-2, and they are other reasons that I prefer the RS-1. The hf-2 has a wider soundstage, which is always a good thing, but it comes at the expense of the "on top of the music" presentation of the RS-1. This is an issue of personal taste and not "better" or "worse", but the differences between the two are very apperant.
Last, the HF-2 does have better tone overall than the rs-1, in that instruments tend to sound more like what they are supposed to sound like. That said, comparitively, the HF-2 drops the tone ball in one area of great importance for me: vocals. Voices on the HF-2 simply don't sound as convincing as those through the RS-1, and that bothers me a lot when listening.
Final thoughts: I like the HF-2 a lot, but it is no RS-1 in my book. It is a great value and I am happy to have it. It isn't going anywhere and it is pretty much what I expected when I ordered.
They are good headphones, to be sure, and I enjoy them a lot, but they are just not of the same caliber as the rs-1 for me.