They now also make the A1 -- which is even better.
"ADL – Alpha Design Labs – creates innovative, smart-looking components for computer-based systems as well as personal and portable electronics. Tokyo-based ADL by Furutech™ aims high using the best materials and innovative design for an expanding line of Japanese-designed precision products including the superb sounding DSD & 24/192 ADL A1 Headphone Amp."
If Iphone 6 plus is 3 out of 10 -- when playing into a pair of GRADO PS-10000e's; then the X1 take it to a 6. The IPOD classic is 1/10 for me -- because it can only cope with lower resolution sample rates.
If you have this then I suggest you think about all the elements you could upgrade to include the quality of your listening experience -- A huge amount depends on the full chain of reproduction:
a) the quality of the original recording -- there are a lot of just bad pressings/masterings and 44hz -- obtaining a good recording and reproduction is the 1st step.
b) the quality of the digital conversion and sample rate -- my minimum target is 320 kbps; however with a good dac I am moving my favourite recordings to at least 24bit/96hz minimum -- or much higher for some instrumental works
c) the player -- be this IPhone, PC or MAC if it is used as anything more than a data-source. Some players, like JR River and Audirvana bipass the computer's sound card and sync directly with the DAC -- it makes a difference
d) the connection from the source to the DAC -- I use an ADL lightning connector to high-speed cable sourced from Custom Cable: The Headphone and Portable Audio Specialists to connect the Iphone to the DAC
e) the quality of your cans (headphones) -- again a huge factor -- no point driving great sound into crappy little headphones -- you need larger drive units and high responsiveness if you want to hear the difference
f) the environment within which you are listening -- RU sitting in a nice armchair next to a fire in a log cabin on top of some desolate mountain -- OR -- are you standing on the metro, in rush hour, with hundreds of irritated sweaty bodies bashing into you -- having to breath-in someone else's garlic and alcohol fuelled supper....
g) the level and type of background noise .......... no point seeking high def playback if your on the metro
h) the volume you listen at ...... it really does make a difference
h) the quality of your own hearing and mental state......... no point paying a bunch for good repro if your a bit "mutt & Jeff" -- i.e. cannot hear the difference. -- or are so pissed at the world that morning that you just are not listening....
For me now - I'm only occasionally am in the write place/head state to use a DAC and my good cans while on the move -- its just as good to have a good set of light headphones with good enough reproduction -- I keep returning to B&O EARPHONES & EARSET 3I when I'm out of the house -- I must be on my 10th set -- I just keep catching the lead.
BUT for in the house -- its the Resonessence Invicta DAC and Headphone Amplifier with SD Reader for me now -- hooked up to my Mac Pro and then analogue out to either my cans or hi-fi, via Balanced XLR - played in my partially sound proofed studio -- WONDERFUL
Anyway -- hope this helps