Edit asound.conf on piCorePlayer

I'm working on a multiroom audio system based on piCorePlayer on Raspberry with Hifiberry amps. It seems to bee possible to split an stereo output into two mono outputs (found on the hifiberry homepage). To configure this I have to edit the etc/asound.conf. I'm not able to edit the asound.conf with the standard user "tc". I need the root password oder super user password to edit. Or is there another possibility to split the amp into two channels?

Thanks
Matthias