[s0matic]

I am contemplating picking up a pair of Sennheiser HD-555's or 595's for home use with my computer. Also, I plan to pair them with a Turtle Beach Audio Advantage Micro USB DAC. I do not plan to add an external amplifier, at least not yet. My questions are as follows:

1.) Which version of the HD-555/595 would be better paired with the Audio Advantage Micro? 120 or 50 ohm?

2.) Also, is the Audio Advantage Micro a good choice as an entry-level DAC for home use, compared with let's say, my onboard sound card (Realtek ALC850), or a separate dedicated sound card (Audigy, X-Fi, Juli@, etc)? In addition, would the Advantage Micro drive a pair of Shure e2c's well, for portable laptop use?

Thanks in advance.