I'm using the Radeon HD 5450 card with CentOS 6.7 running the 2.6.32-504.30.3.el6.x86-64 kernel. The PC goes into a reboot loop shortly after the grub boot screen comes up. I found that we can get the PC to boot up all the way by adding the nomodeset parameter to the kernel line. The problem with this solution is that it won't recognize individual monitors once the system is up. It shows only a single generic monitor in the setup instead of the two that are attached.
I tried a couple of earlier CentOS releases and found that release 6.5 with the 2.6.32-431.29.2.el6.x86_64 kernel works without issue and recognizes both monitors with no additional tweaking required. Based on experimentation with a couple of other Linux distros, it looks like anything after the 2.6.32-431.x kernel won't support this Radeon card.
Has anyone else run into this issue and, if so, found a way to get multiple monitor support with the newer kernels?