The WIN 8.1 driver is buggy .. WASAPI MODE needs manual setting to match each music file's nitrate... Not auto! The ASIO DRIVER works better... Auto bit rate works..
You have to connect the USB cable between M8 to the laptop and switch on the M8 and then you boot up the laptop. Sometimes if I power the M8 LX to the optical and then back to the USB mode the laptop will recognize the M8; sometimes NO! BUGGY ....
With U900, lowest gain will sound fine , my HD800 needs mid Gain to work.
I have even a 1/4 inch TRS to RCA MALE and connect to my tube main rig. Set the M8 to highest gain. The main rig sounded real good through my tube mono bloc amps and Fostex crossover less Horn speakers.
Just for fun, I rigged up a RCA to female 1/4inch TRS plugged(DIY)
my HD800's into my Tube preamp output !
Wow tube richness but at the expense of a bit of speed and impact compared to direct connection to the M8 LX
I will post a full review of my experiments when I get back from my overseas trip as my experiments were cut short by my overseas trip.