Power Connection Questions on parts in front of me

[Aviewanew]

Parts:
- Gigabyte GA-EP45-UD3P motherboard ( http://www.gigabyte.com.tw/Products/Motherboard/Products_Overview.aspx?ProductID=2919 )
- 1.6 gHz Celeron
- 2GB Patriot RAM (2x1GB)
- MSI NX8400GS PCI-Express Video Card
- 6x 1TB Drives
- Antec SL400 Power Supply (from an old machine) ( http://www.antec.com/specs/sl400_spe.html )

The Antec has a 2x2 and 2x10 Power Cables
The motherboard has 2x4 and 2x12 Power Connectors

I can put the 2x2 into the 2x4 Connector, and the 2x10 into the 2x12. But I can't find online if that's acceptable to power the system.

Everything I see says both connectors are backwards compatible, but it doesn't tell me if using both in backwards-compatible mode is workable.

 

[IH8U]

I'd suggest a new PSU, however Antec is a good choice.

http://www.newegg.com/Product/Product.aspx?Item=N82E16817371002
$60 (Antec 550W, free shipping)

*EDIT* you might want to think about a 650W, I just noticed the number of 1TB drives you were using.

 

[Aviewanew]

I'm looking at this Power Supply now: http://www.newegg.com/Product/Product.aspx?Item=N82E16817371015
On sale today for $50

It has a 2x4 connector (it says so in a review) and it has a 2x10 connector with a 2x2 addition (as seen in the photo).
However, the connector shapes look the same as the one I have; and the 2x2 does not fit into the 2x12 motherboard connector alongside the 2x10 from the PSU.

I don't really understand that.