I guess the issue is lack of drivers for the Radeon graphics unit. I havn't done this myself but suspect getting COS installed and running requires something like the following steps:

1. Disable the radeon graphics unit in BIOS (I assume that is possible - I don't have an A6 myself)
2. Install COS
3. Find and install AMD's latest linux drivers for radeon graphics for RHEL 7.1 (or 6.6 if that is your choice). Its available from AMD here
4. Enable radeon graphics using AMD's Catalyst software.

You may need to do a bit of experimenting but it should be quite possible.

Cheers

Peter