An interesting info for all iPhone and iPad owners: since 2013er firmware update of the HRT MicroStreamer worked fine as a DA converter to the i-devices. Unfortunately, only with standard resolution, ie 16bit, 44kHz. HiRes files were indeed played / changed, but overlaid with a strong roar. Apple has reworked at the drivers: since the update of iOS 7.1 to iOS 7.1.1 also works playing / converting HiRes files to 24bit and 96kHz! The MicroStreamer shows the resolution also bravmit the lateral LEDs.
In other DACs, eg Fiio E07K has even before the iOS 7.1.1 update works with the MicroStreamer not. but now!
Tested and working configuration: iPhone 5S or iPhone 4 -> Apple MD821ZM / A Lightning to USB Adapter -> Cable USB A male to mini USB B male -> MicroStreamer -> headphones or line out to the amplifier. There is no USB hub is necessary!
As playback software I use iPeng 7, the music will be streamed so from my NAS on the iPhone / iPad. But sound improvements are already in play from the Spotify app available.
The sound I judge with various high-quality headphones, Beyerdynamic T51P, AKG 701, Stax, ...