- I'm using 2x 64GB (Class 10 / UHS 1) Sandisk cards and haven't had issues with scanning itself at least, separately from the naming/tagging/artwork issues.
- I have ~5000 songs for now between them, and usually I get the spinning wheel for less than 2 seconds when I navigate around (mostly either album view or occasionally the direct folder navigation)
- As far as I understood the whole impedance issue, it only affects negatively IEMs with drivers that have (strongly) non-linear response curves, and thus at the higher impedance level react unpredictably. Shouldn't any halfway decent amp have a clean linear, flat response and thus not be affected by the impedance level in that way? And the only difference between the original and modified AK100 would be a perceived higher gain at the same (max.) volume setting on the AK100?
- I have an E17 myself and like it fine for what I use(d) it for, but I haven't heard a single of my headphones & IEMs (incl. theoretically "bad" matches) sound better through it than straight from the AK100, actually most that require more omph sound worse and more distorted when pushing the E17's theoretically louder output vs the AK100 which still sounds clean even at max. volume (as it should, given its price). If you really feel the need to amp separately, I would suggest getting something higher-end.
Generally though, when it comes to higher-end equipment other than the actual headphones, I'd take any claims of night-and-day differences in sound quality ("great" vs "unlistenable" etc) with a biiiig grain of salt around here (i.e. audiophile forums, not just this particular thread or subject) Don't forget to give -yourself- enough time to enjoy and listen to the music and equipment before worrying spending more $$$ to "fix" or improve things...