Based on your personal preference, X7mkii sounds like the best price/performance ratio. If detailing is not what one favours, then X7mkii could be the best dap for its price. Am I right?
The difference in price between X7mkii with AMP5 and DX200 with AMP5 isn't quite that big, and it really boils down to how you like the design of each, the firmware, and who you trust more with their support.
Both iBasso and FiiO are outstanding and I grade both in the golden companies range, both will help you with your issues and both offer great price performance ratio.
+ The sonics of DX200 have slightly more detail, and are slightly more dynamic and vivid.
+ The screen quality is better on DX200, larger display, better color contrast, better max brightness (outdoors usage), better general detail
~ UI and firmware navigation will be a matter of taste
~ Device looks and aesthetics are also a matter of taste
~ Volume wheel and usage are also a matter of taste
~ X7mkii has something similar to Lurker's mod, but on X7mkii it costs money, so some of the cost evens out if you want to squeeze all performance there is
- X7mkii has 2 mSD slots, if this is important to you