If I have a mixer or interface with multiple i/o's how does it work with a DAW?

For example, suppose I had Line6 UX8. I'm going to record a whole band at the same time, so I'm going to use all the inputs.

How does the interface "interact" with Sonar for example. Does the program let you open up 8 tracks, arm them for recording and record them seperatly in the program?

I guess my confusion is, can 1 USB cable carry the audio signal of 8 different inputs that are separate before going into the interface, "join" in the USB cable and separate them again as 8 different tracks into the computer or DAW?

PS. Can this keyboard work as a midi controller, it doesnt have MIDI I/O but it has a USB out?

Yes, that keyboard does MIDI. It says so in the description a little ways down the page. As far as transmitting that many signals, yeah you should be able to do that. I'm not too familiar with the UX8 but it should be fine. I heard somewhere that USB can only do two channels at a time, and you need firewire for more, but I'm pretty sure that's total BS. I know that most interfaces that advertise 8 channels are going to give them all separately, unless you're talking about a mixer (which isn't an interface) and won't do that.
Telecaster - SG - Jaguar
Princeton Reverb, Extra Reverb
P-Bass - Mustang Bass
Apogee Duet 2 - Ableton Suite
yes, otherwise it wouldn't have had 8 inputs

Guitar Rig:
Epiphone Les Paul Standard
Godin Freeway
Korg DTR2000 Tuner
Axon Ax100
Hughes & Kettner Triamp Mk||
Boss V-Wah, CE-5, TR-2

Bass Rig:
Ibanez sr700
Ampeg BA600/115
Boss MT-2