Loquah
Headphoneus Supremus
I can't directly comment on the DX50/C5 combo, but I think olddude can help there (among others no doubt). What I can tell you though is that you will absolutely not need an amp with the DN1000s. My reason for using an amp is one of synergy and flexibility because the E12DIY lets me change op amps to suit the 'phones I'm using, but it's absolutely not needed and the X5 is a stellar device all buy itself.