I dont know which one to get. My main concern is the sound quality. I will use the ath-m50s with it.
Fiio x3 will definitely work as a dac/amp with a laptop/pc. Before plugging the x3 in, change the USB function setting on it to "DAC" (instead of "USB"). You may need to update to the latest firmware I'm not 100% on that.
I have both the x3 and e07k and I feel the x3 is the better one of the 2 mainly due to the more powerful amp.
Personally however I prefer using the e07k docked into the e09k.
The 3 devices listed above both use the same Wolfson WM8740 DAC. However, to my knowlege the E17 has a more powerful AMP. Since they both use the same DAC they will sound the same using it as a DAC. I would say it is a huge upgrade to the standard laptop/mac you will be able to hear the difference right away.