I have the HM700 with me now - I don't want to comment too much on the SQ yet as I haven't had nearly enough time with it but suffice to say it compares very well with DAP of the same price range. I thought it might have been RockChip based but I was told it indeed runs on SigmaTel. In fact, it is possible to RockBox HM700 as the same SoC has been RB'ed before on other DAP. Of course, it also depends on whether there will be interest from the RB community to do it. For now, you can expect all the basic function from your typical SigmaTel based DAP. But if you want gapless or EQ, you will have to wait for someone to RB it.
Also got a chance to listen to the upcoming HM802 - it sounds quite like HM801 with a warm, textureful and euphonic presentation, but with the upgraded new UI.
Mind if I comment about the non-sonic aspect of the HM700? I'm not too familiar with the RE-x00 series of IEMs bundled so it's gonna be hard for me to make any sonic comments.
I'm kinda impressed that the HM700 is being sold for $259 with the RE-400B, and $499 with the RE-600B. Although the output socket is balanced, my Oyaide plug works fine with it but Dr. Bian said that it'll depend on 3.5mm SE to 3.5mm SE.
I like the very simplistic UI with the hidden buttons under the black panel. It took me while to use it though to determine the pause/stop button. There is no middle button but just the four (top, bottom, left, right). The middle orange buttons are easier to use.