I'm looking for your opinions which will bring me the "best" sound. I already own a TTVJ portable AMP/DAC which I hook up to an iPhone 4 via an ALO connector. I'm wondering if a iRiver AK100 (or ColorFly Hifi C4) will bring me better sound? I will need to get higher quality files of course. But all other thing equal, what will be the best in your opinion?