To P-A-P and others interested:
I am a new head-fi member, been lurking on and off for a few years and gotten a bunch good advice and information from head-fi, so thought to contribute a bit on this.
Having sought for about a year for a good kit to take my music with me to the office and when travellin I am now a happy owner of:
Ipod classic 160GB (ALAC)->istreamer->corda stepdance->pioneer hdj-2000.
Soundwise, I am not a real expert in analysing the sound and comparing it to other set-ups as this is my only first real full portable rig, but the words that come to mind when comparing the rig to ipod->corda stepdance->pioneer hdj-2000 are: deeper, punchier, clearer bass, more detail, more precise soundstage and clearer more pronounced highs. The bass is actually so plentiful with the pioneer headphones that I changed from the original pleather type to velour pads to tone it down a bit. With my Grado RS-2 the highs were maybe a bit too much, but work alright with the pioneer as it has somewhat reduced highs even with a quarter mod for the pads.
This is now my portable kit, as I also discovered that I am indeed able drive the istreamer with MiLi Power Crystal external battery pack that feeds it via USB mini at 5 V and 1000mA. The bass may become a bit mushier when the battery is less than 1/3 full. Maybe the 1000mA capacity is not enough as the USB power supply that comes with the package feeds istreamer with 2000mA at 5V.
The istreamer eats through the whole 2000mAh 3.7V battery in about 3-5 hours of continuous listening based on my first experience, so now I am getting one with 5000mAh 3.7V battery. There are ones with higher capacity, at least I found one with 5000mAh 5V battery inside, so that would give even longer life time. So far I found none with higher current output than 1000mA which might be required to get the full sound quality if I am correct that the MiLi is struggling with supplying enough current.
The full set-up wrapped together on top of each other with elastic strip (not sure about the correct English word, this cloth strip thingy with properties like rubber bands) looks pretty awful actually what with all the different form factors and looks of the devices and cables sticking out here and there, and would probably scare airport security people, but its the sound quality that matters, right?
Disclaimer: If you decide to experiment like I did with these external battery packs as power source for istreamer, then you do it at your own risk as I cannot guarantee that it does not harm the istreamer (and the manufacturer has nowhere hinted at this option), or in any way propose that you go the way I did. For me it seems to work so far, but you never know...
PS. Yeah, I know, my wallet is already hurting...