1. All it needs is a PCIe x16 slot.
2. Depends on the machine. Some disable, some don't. You have to ask the motherboard maker. As this can change with BIOS version and settings, you don't know for sure. It's usually a non-issue.
3. Not suggested. The prior comments say to forget crossfire on APUs and use the GPU.
4. If an ATI card doesn't work, get an Nvidia. That's what I do.
The GPU you noted is not a light tap on the power supply. Be sure you have a spare 150Watts on the +12V rail you tap.
So I thought about upgrading my PC, I would like to add a new GPU, the R9 380x. However, I have an APU A10-6790k. My motherboard is the MSI grenade A68hm. Now I read some stuff about the APU's working with crossfire with graphic cards so here are some facts and worries:
1. My motherboard is not known to support crossfire
2. If I add the GPU, what will happen with the APU? Will part of it shut down?
3. Can the GPU I would like to have work with my APU?
4. And finally if it just doesn't work, what suggestions do you guys have?
Thank you in advance!!