The FIIO E09K is technically a headphone amplifier but you can also plug in active monitors (the JBL's you're getting) The E09K would definitely help with your headphones as it would give them more power making them sound A LOT better. E09K is not portable.
The E17 however is portable and with an additional Line out cable (Amazon search for FIIO LOD) you could hook it up between your Ipod and M50's.
The E17 is an Amp and a DAC (think external sound card) so using that with M50's and IPOD when you're on the go will make a substantial difference in sound.
The E17 can dock into the E09K at home which would then cause it to be AMP/DAC for your head phones and allow you to plug the JBL's into the E09K to act as a sound card for the speakers.
Not only is the E17 not a bad DAC/soundcard but it's external from your computer so it's not prone to interference that can come from your computer (blips and bops you can sometimes hear when listening to things).
There are better AMPs and DAC's out there but these a pretty good to start off with at a not insane price point (around $200 combined for E09K and E17).
The Hosa cables are pretty good. No point in spending more for cables than that as i'm of the belief that a relatively cheap but well made cable (such as hosa) is just as good as $200 cable that does the same thing. What will cause the noticeable difference beyond the speakers is the addition of a DAC instead of the integrated sound card.
Lastly, IF you should decide to take the plunge and pick up the FIIO E09K and E17 then you'll need a different cable to plug into your speakers instead (search amazon for Hosa cpr202)
The world of audio is an expensive place! 5 years ago i couldn't imagine spending $300 for headphones, then i got the Q701's... Once you hear good sound you can never go back :)
Edited by Scabertrain - 1/20/14 at 3:05pm