I got a Mogami 10 foot extension cable for my 400i works nice and I do not hear any difference in sound. Got it for 71 dollars on Amazon. I have a question about the 400s. I have noticed that my 400i When plugged into my s7 volume is not that high. Even when turned up. Thinking about getting the 400s for playing with the s7. Does anyone know if it would be worth it? Thank you.
I would look at another source (DAP) like a Fiio X3ii instead of getting a second headphone. Or do you need another headphone? I don't use my HE-400i as a portable but my X3ii and older X3 drive them to fairly loud levels.