Asus XONAR U5 SI User Manual page 16

Connecting 4.1 channel speakers / power amplifier
Amplifier
No
1 Front Out port
2 Rear Surround
Out port
16
OR
Item
Connects to the front input port of 4.1 channel speakers
Connects to the rear surround input port of 4.1 channel
speakers.
ASUS Xonar U5 SI User Guide
Description
Mic/Line-in
Headphone
1
Front
Center
2
Rear
S/PDIF