I'm trying to think between HeadRoom Total Airhead/Bithead (100$) and Fiio E7 (76$)

Im only going to use this as a headphone amp for Ipod listening with my headphones
not a DAC (Digital-to-Anagol converter) for my computer or computer amp.

My Ipod will be connected to a line-out dock (SendStation) for better sound quality
and my headphones are a Sennheiser HD 518 (50 Ohms Impedence)

I dont care about the price as much as long as it is under 150$

Which one should I pick and if you've ever tried out any of those amps. Which one delivers better sound quality? Which one is more suitable for 50 ohm output impedance?

Which affects the mids? Highs? Lows? Bass? More.

I've read many review on both and they all have their flaws but I'm looking for one that makes that most sound quality difference (not just volume) without major distortions.

If you have any other brand or amp recommendations that can power 50 ohm headphones clearly I would appreciate it.

Please answer if you know what you're talking about and/or you've had experience with both these amps since I dont want to waste money for minor changes in sound quality than just regular cans. I'm having major trouble deciding which sound system would be the most premium for listening to my Ipod at home.