Sorry, I haven't tried the X7 yet. I haven't seen any demo on the shops here. You sure you need more than 32GB+32GB space when you're using it on the go?
I really much prefer J3 for portable use because of the size and it's versatility like easy-to-use buttons, EQ with BBE and interface. And there are available customized GUI made by one of the headfiers here. PM Kizune or check out the J3 Appreciation Thread. I believe that it sounds good even without an amp. Although, I never heard Sanza Players or Sflo or other portable players. But I can compare it to my other rig (Ipod Classic->CLAS->MK2 with ALO interconnects), and it can hold on its own due to portability and EQ to my other phones. Though some may have different experiences compared other players/DAPs, they may agree/disagree with their preferences as well.