I have RH-A30. Will do a review some day, but for now I will just say they are good. I compared them in shop to ATH-M50, and I preferred them. It's because RH-A30 sound IMHO cleaner than ATH-M50. In shop I used Beethoven 3rd symphony, and Airport tune from J. O'Callaghan Subculture album.
First I tried ATH-M50 and played the symphony. I was really impressed with the sound ATH-M50 produce that I couldn't wait to see how RH-A30 will do, and so I tried them next. After just first few seconds I already noticed RH-A30 sound cleaner, more transparent. The high treble range on ATH-M50 to me sounded quite uncontrolled and imprecise, while on RH-A30 they sound extremely accurate. To put it in simple terms - I was in shock that cans for 200 euros can sound so good. Then I tried trance tune expecting some problems with low end, but I was surprised again - the low end was very present and well controlled. I just bought them and continued listening at home.
I find them very hard to use with pop music, because most of pop is badly mastered, and on these cans you will hear all that. Apparently both classical music and electronic music are usually well mastered and in that case it is a genuine pleasure to listen to. I use headphone out of my NAD744 toslinked and set to Tone Defeat off course. I tried also headphone out of PMA500, but the I didn't like the soundstage. One that I get from NAD is really extreme, something very unique.
On these headphones the difference is easy to spot. Just lunch some game with 3D sound and you'll see how easily you can point out where the source of sound was. Not only direction, but also distance, you just know exactly where the sounds are coming from. When listening to symphony orchestra you will easily know where each section was located relative to microphone used for recording.
RH-A30 are my current favorite headphone. Before I was considering getting HD600, but now I just know it's not going to happen, because these cans sound better.