As the title says, I have switched the cables between the ODAC and O2 and removed the gain resistors R17 and R21.
Switching the cables may sound very easy, and I had expected it to take no more than a couple of minutes to do. I was wrong. Very wrong... It took me about 40 minutes in total because removing the wires was hard and then getting them back on was even harder. The holes had been messed up so I had to surface mount the cables on the back of the ODAC with a lot of solder to keep them in place...
Removing the gain resistors was easier though. It was pretty narrow but I could fit a tweezer between the resistor and the board. Then I heated up the joints on the back while pulling with the tweezer and eventually the joints let go of the resistor and it flew away through my room :P Now the gain is on a better level, no noise at all, even with the volume knob turned all the way up and there should be less distortion, especially in the higher frequencies.
Now when I have proper stereo sound everything sounds incredibly good and even if this amplifier costed 4000SEK (that's about $600/€480) it's still a very good buy.
I'm planning to sell this one though. Make some profit to buy myself a proper DMM and some soldering equipment. Remember I have only borrowed the soldering stuff from a friend, for a couple of months now. Should buy him some gift too for the profit I make. Then I'll build two-three more and keep one for myself and sell the rest. I'll be selling an Asus Xonar STX soundcard soon too, because as far as I can hear the O2+ODAC beats the STX.
Do I sound happy and satisfied? Yes, of course I am!