Thanks again SaLX and Evshrug. A follow up question though... How about the O2's gain settings in relation to the Mixamp - meaning the O2's standard 2.5x gain is stated to be meant for 2v desktop sources and the 6.5x gain for .5v portable sources. The Mixamp is rated at 1.6v, but is that not at max volume? I don't know that running the Mixamp full out is the right way to set it - I think around halfway or a little less would be ideal to reduce hiss. So at 50% volume its voltage would be down to around .8v, which I believe would be suitable for the 6.5x gain setting on the O2 from what I've read. Then don't forget the power draw from using a mic, which I would like to do. I will order the O2 with the 1x/2.5x gain option since that is the recommendation I've gotten here but please let me know if my concerns above make any sense.
I just wanted to reformulate my question for the sake of clarity... I'd like to source match the gain options of the O2 I'm ordering with the needs of the Mixamp. I read the Mixamp is USB powered and maxes out at 1.6v (70mW @ 32ohm). If the sweet spot on the Mixamp's volume dial is around 50% would the voltage not also be cut almost in half? I would think gain needs to be higher than 2.5x to match up around .8v from the Mixamp. I've read the 2.5x gain from the O2 is for desktop 2v sources and the high gain option is for lower level sources around .5v, which it looks like the Mixamp would be if used at around 50% volume. My concern with selecting 1x/2.5x is not having enough gain when using the Mixamp at 50% plus powering a mic. Is my thinking correct?