Which still sort of defeats the purpose of having such a tiny music player, doesn't it?
Clip's amp is nearly perfect for portable headphones like M-100: 1 ohm output impedance, 15 mW maximum power, less than 0.05% THD, and almost laser-straight frequency response from 20Hz to 20kHz. If you really, really need the power then E5 is probably a better choice than E6. But really, M-100 doesn't need the power.
Totally agree. Just throwing it out there ;) I use mine as a beater DAP with a set of Amperiors/Koss KSC75s for when it's raining or snowing out. Buttons are so much nicer than touch screens for those situations. If the thing breaks...who cares? $20 bucks later you've got another one in pocket.
I will say though, the audio quality of the Note 3 stock is pretty decent on its own. The Qualcomm WCD9320 seems pretty well implemented. It's sound quality seems pretty comparable to my Clip Zip with efficient phones. (Chokes a bit on anything 250 ohms and up with medium/high sensitivity...but that's certainly *not* the M-100s.) I'm not certain there is much if any audible improvement there with the Sansas, but IMO you should get one anyway just to save wear and tear on your phone. They really are great.
As far as these go, using a DAC/Amp via USB On-The-Go, the C5D isn't a bad option from a portability standpoint. That thing is wonderfully small. My personal recommendation: I'm a huge fan of the Leckerton UHA-6S.MKII. Cons: It is chunkier, both in thickness and weight, than the C5D and that may be a turn off. Also, It only does 16/48 via USB connection.
However, using Opamp AD8610, I've never had a moment of cellular interference on GSM with my Note 2 dual locked right to it. It has extraordinary battery life; I've gotten over 24 hours of use on it between charges. Most importantly: the Leckerton's implementation of the Cirrus CS4398 DAC was a big upgrade sound quality upgrade over my Note 2's WM1811, even with custom kerneled. Nick Leckerton works for Cirrus Audio, and he through careful implementation really got this thing to really sound great.
At $150, I don't think that the E18 is worth it. By that price point, you're looking at a dedicated player (and the ones that Ratinox recommended earlier in the thread are all spot on). If you're still looking at using your Note 3 as a convergence device shop used on the forums for a nicely cared for Leckerton or C5D. IMO Rock the Note 3 for a bit longer, save up, and decide on which direction you want to go.