4.What is the difference between the X7MKII and X7?

1. Some basic specs comparison:  http://fiio.net/en/products/71/comparisons          

2. Storage: 
X7MKII: 2GB RAM, 64GB Internal Storage, 2 Micro SD Card Slots
X7: 1GB RAM, 32GB Internal Storage, 1 Micro SD Card Slots

3. Chips Schemes
A. X7MKII utilizes the DAC chip ESS9028PRO-the high-end chip pf ES9028 series. Its signal to noise ratio goes up to 129dB and THD+N reaches -120dB. Higher resolution brings wider sound filed and sound range as well as improving the sound quality.
B. X7MKII comes with 7 filter modes while X7 comes with 2 filter modes. (Filter modes are bulit in the DAP chip itself.)
C. The X7 Mark II utilizes three separate crystal oscillators This guarantees that under all sampling rates there is radically reduced jitter, increased clock precision and stability, and overall more correct conversion from digital signals to analog.
D. When combined with the ability to skip Android's native audio resampling (ASRC) along with the ES9028PRO's unique THD compensation feature and special built-in filters, the X7 Mark II ensures that your music will sound sweet and musical, just like how it is supposed to.                          

4. Buttons&Ports comparison: 
A. X7MKII could adjust volume via volume wheel, while X7 needs to use "+" and "-" buttons on the side to adjust volume.
B. X7MKII supports Optical output, Optical/Line/Coaxial Output at a shared port; X7 doesn't support optical output, Line/Coaxial output at a shared port. 
C. X7MKII/X5III has two hidden micro SD card slots on the right side of its body while X7 has one plug-in micro SD card slot on the left side of its body.
D. The power button of X7MKII is on the top of its body while X7's is on the right side of its body.
E. X7 could switch the button mapping while X7MKII couldn't.
F. X7MKII employs the GFF screen while X7 doesn't. 

5. Charging:
X7MKII supports the mainstream quick charging protocols like BC1.2, MaxCharge and so on.
It's recommended to use DC 12V/1.5A, 9V/2A charger to charge the X7MKII/X5III. Of course, X7MKII/X5III also supports DC 5V/2A chargers.
X7 doesn't support quick charging. It's recommended to use DC 5V/2A charger to charge X7.

X7MKII supports 5GHz and 2.4 GHz while X7 only supports 2.4GHz.

7. Bluetooth: 
X7MKII supports Bluetooth 4.1 and aptX while X7 supports Bluetooth 4.0, and aptX (X7 needs to be upgraded to Android 5.1)