I am very happy with the MSII (the base model), but I havent heard the other Streamer models. Surprised by the number of people here who still turn their noses up at USB DACs - they really need to read some of Gordon Rankin's posts over at Computer Audiophile before coming out with pronouncements re. USB vs coax vs Firewire etc. Implementation is everything, and the lollygaggers who get caught up in reciting outdated 'wisdom' will inevitably get left behind in the coming decade.
Not sure that the dual-RCA-into-mini-plug arrangement that you need for most portable amps will make everyone happy, but I like what it has done for my music. If I had to describe the sound signature in a single word, it would be 'smooth' : those looking for extreme clarity/resolution etc would be happier with another DAC. Comparing the Streamer to the Benchmark/QB-9 etc is farcical, but its surprising how many people want to engage in this type of madness. Those who want a Ferrari need to be prepared to pay for one :)