Adding two HDs to 8700

Dell XPS 8700  x64, Win 7 Home Premium, BIOS A06

The XPS 8700 provides for three HDs. My unit came with one HD and I plan to add two more.

Before I open the case and start plugging things in, I'd like to have as much information about the task as I can gather.

I learned that some people have a problem with the OS recognizing the new HDs which requires some manipulation of the BIOS (EUFI to Legacy and back again).

There was also a question about which SATA ports should be used. The primary drive on my 8700 uses SATA 0; the optical drive uses SATA 1.

I appreciate any help you can provide.
EdP