I know that that istreamer takes a pure digital stream from the ipod and then uses a dac to convert it to analog. This is a pretty complete review:
http://www.avguide.com/review/high-resolution-technologies-istreamer-dac-playback-40. I think that the technology behind this is not straightforward and that not too many devices are capable of doing this (peachtree makes a few devices that do this, cypherlabs makes a portable device). I have not heard of the pure i 20 and if it does this for a $100, it would be a world beater. I'd like to read more about it before buying one since my understanding is that it is no mean feat to extract a pure digital signal from an ipod. In any case, I use an HRT musicstreamer ii in my office set-up and it clearly improved the SQ of my computer based music system. I have not heard the Musiland monitor but I know that Pacific Valve makes good products; it does take a proprietary driver, though, and I'd rather not be dependent on a third party to update the driver when needed. The HRT musicstreamers do not need a special driver.