My video look and initial analysis of the HRT iStreamer DAC which gets the actual digital-only output from i-devices and converts that to analog to feed to amplifiers for headphones or loudspeakers.
When I first connected the iStreamer I was pleasantly surprised that it interfaced perfectly with my iPhone4s according to the instructions with no extra effort. I use the iStreamer power cable and Apple cable to connect the iStreamer to power and to the iPhone, then a Belkin RCA to miniplug cable to connect the iStreamer to my Objective2 by JDS Labs headphone amp. The volume on the iPhone is still active as are the EQ settings, and the connection to the iStreamer defaults the iPhone volume to maximum which is highly desirable. It does not change the EQ settings though.
When I discovered that the EQ settings were still active, I wondered if the analog signal from the iPhone's dock connector was being passed through the iStreamer instead of the digital signal, as though the iStreamer were not reading the digital signal due to some glitch in the connection. Apparently the Apple i-devices embed the EQ settings in the digital signal, so the iStreamer is reading the true digital output from my iPhone, and then in the process of converting digital to analog it somehow applies the EQ settings if they are active at that time.
I agree with HRT (who make the iStreamer) that it's best to have the EQ settings set to Off (not Flat) to get the cleanest possible sound, but I also think it's important to have EQ available from the i-device in cases where the need for EQ outweighs minor differences in distortion, and where EQ is not available elsewhere in the playback chain (i.e. my headphone amp has no such controls). A perfect example is my Philips L1 headphone, whose heavy bass sound is not workable for me without bass reduction. Comparing the sound of the L1 through the iStreamer with and without bass reduction, 'with' sounds much better in spite of any added distortion from the EQ controls.
Using a better headphone with EQ turned off, the difference between the sound without the iStreamer (iPhone connected to headphone amp through the Line Out Dock [LOD]) and then with the iStreamer connected was softer somehow, as though some small degree of harshness disappeared. Normally I wouldn't expect to hear such a noticeable difference when adding a new device to the signal path, but given the increase in resolution from bypassing the iPhone's internal DAC, if there weren't a lessening of distortion the extra detail would not be as enjoyable.
I don't have any other comments on the sound, since the iStreamer is an electronic component that's much closer to the ideal "straight wire with gain" than a headphone or other transducer would be. The best way to appreciate what improvement it makes (hopefully!) is to listen with it connected for a good while and then listen without it and hear for yourself. For me, that makes a much bigger impression than the other way around, i.e. listening without it and then inserting it into the playback chain to hear the difference. Without it, the sound seems to lose a lot of life.
I could use another 500 words to describe 'life', but I don't think it would make things any clearer - listening is really the key. The best analogy is to take a beer out of the fridge and pour it into a glass, then let it sit long enough to go flat. That's not the kind of 'flat' you want in a hi-fi system, but that's the analogy to not using a separate DAC with Apple i-devices.
Physically the iStreamer is about the size of the iPhone4s, but twice as thick. The iStreamer is enclosed in a strong pebble-finish aluminum case which probably won't show scratches unless seriously abused. It feels fairly dense, but not as dense as the iPhone. On one end are the outputs - left and right channel RCA jacks, with the right channel coded in red. On the other end is the mini-USB power jack, the standard USB jack for the Apple USB cord, and the 32k/44k/48k signal lights (3 small LED's).
HRT supplies 3 cables: A thick power cable that connects to the AC-to-USB power box they also provide, an Apple-style USB cable that works OK (but I would be inclined to replace if I can find a better one), and a double-ended stereo RCA patch cord that I think could be eliminated since I use an RCA to miniplug cable to connect the iStreamer to my headphone amp. Many headphone amps do have RCA inputs, but I'd suggest that whichever cable type you need you'd be better served with an audiophile-grade cable to connect the iStreamer to your amp. I don't see much issue in connecting an i-device to a desktop stereo since the desktop would most likely have its own music server with more features and storage capacity than the Apple i-devices.