One of the biggest issues when people compare is that they never volume match, or they do it by ear (ie highly inaccurate). The only way to make a valid comparison (even acknowledging that its highly subjective) is to volume match as closely as possible - then a/b.
It's pretty easy to do too - all you need is an spl meter (even an app with a smartphone is better than nothing), a constant tone (I use 1 khz test tone), and a set-up that allows same placement of microphone each time.
Its amazing how many formerly perceived differences disappear when the volume on two devices is exactly the same.
FTR - when I had it, I loved my Arrow with just about everything - including the HD600. I sometimes think that I may have been far better off just sticking with a 64Gb iTouch4 + Arrow - than moving into the changing world of the new HiRes players. If Apple came out with a 64Gb Touch with expandable memory, or a 128Gb version - I'd just repurchase the Arrow, sell my other DAPs and I'd be done