I just solved it. So, when i was trying to fix it first i did a bios update to F13. It did not work. Today i tryied the BETA F14d Bios and the system booted with the ASUS on the PCIE4X and my 5870 on the PCIE16x. it first did not recognize the board and would not install the drivers because of that. I shut off and went back into bios and disabilitated the AUDIO on board. It than found the XONAR na let me put the drivers. It was still time consuming to put all things working, the microphone you have to find where you choose back panel (if you use the back microphone as me). Also, i tryied to put the on board áudio back and it worked both together, but than i got it disabled again (theres no reason to have both).
At the end the conclusions :
1- Its not ASUS fault , its the GIGABYTE MOBO BIOS
2- I read that sometimes the dual bios interchange some data, so im not sure if it was the F14d or the fact that i have donne 2 updates (so like the 1st was F13 and the other bios went to F14d, so both updated)(just my thinking ...)
I hope no one has to waste so much time as i did about that. Just update the Bios.
Good to hear!