Firstly kudos to iFi for the hip-dac, it is an excellent amp/dac and is one of the best upgrades possible for a mobile phone or even a DAP. I've tried the three latest firmware's now. There is 5.2b 'limoncello', 5.3 standard and 5.3c GTO. Between 5.2b and 5.3 there isn't a lot of difference, perhaps 5.2b is a little cleaner and 5.3 a little more 80's, 90's retro....but it's a tiny difference and both sound fantastic. The 5.3c GTO has less ringing and delay so is 'cleaner' but to me sounds more digital and is not for me......it's too sharp. The 5.2b and 5.3 sound organic. Some though who want a crisper, cleaner sound, will like the 5.3c GTO a lot. The hip-dac is quite different to the FiiO sound and for someone like me who had 80's and 90's hi-fi, the hip-dac is a sound I am used to and like a lot. I've bought a lot of IEM's and headphones in my time, but the hip-dac is a real, and maybe better, upgrade for all my IEM's and can drive all with plenty of juice to spare.....plus it looks beautiful.