Actually what you're looking for is no less than a 1:8 impedance match - as it can affect the damping factor. Basically this can mess with the frequency curve if the damping factor is too small. In easy to understand terms, it can cause the headphone to either under-represent or over-represent parts of the normal frequency. An example of this is the K701 where an incorrect damping factor can audibly change the bass response. In your case - your 4S has under 2 ohms output impedance - so any headphone over 16 ohms should be good - including the Momentum. Using the Galaxy S4 though - if the Momentum is 18 ohms - may not be such a good idea (would pay to check with Sennheiser - they'll know if it's likely to change or not).
The 1:8 rule is a general (safe) rule of thumb. Depending on the headphone - this factor could be less. But for your set-up ....
4S is under 2 ohms so pretty much any headphone will be OK (as long as the 4S can power it)
Clip Zip is approx 1 ohm so again pretty much any headphone will be OK (as long as the Clip Zip can power it)
**Sorry - originally I thought you were talking about the Galaxy S4 - I should have read initial post better**
If your pout put impedance is 4-8 ohm, and you're trying to run a headphone with known frequency issues with damping that is lower impedance than the 1:8 rule - then adding an amp with a low impedance out is one way of correcting the damping mismatch.
No problems - only dumb question as far as I am concerned is the one you don't actually ask. Better to inquire - there is always someone here willing to help. BTW - this thread may help with understanding damping factor (http://www.head-fi.org/t/607282/headphone-amp-impedance-matching-basics-you-need-to-know)
See a much better answer there. I forgot to mention that an amp would resolve your issue... that being the case. Let's assume you need an amp. A Fiio E6 is a nice place to start although I recommend you try to find an E11 used for about the same price as the E6 is new. Granted though that is more to carry around,
Still there are many headphones with a sound simmilar to the Momentum, that do not have it's low impedance. For Example the Akg K550, although it may not have enough bass for you, And you still need to decide
if your need isolation
if you want open or closed headphones [the first question kinda answers teh second]