wow Gizmo, I was in audio for a living for 7 years and the way you worded that was really confusing even to me...
If the manual says:
"they are stereo left and right and can be used with unbalanced cables as well. But as I see it in the manual the only time they want you to use unbalanced cables is when you are in bridged mode."
Then that means they are mono, TRS inputs. Or balanced, mono/single channel connections. And together, they make up the left and right inputs. The connections can accept balanced TRS cables, or unbalanced TS cables. TS and TRS are the same cable, TS just has a signal and ground connection in it. TRS has tip, ring, and sleeve, which is how it gets the balanced signal across. I think "tip" is negative, "ring" is positive, and "sleve" is the ground. Honestly I dont remember what pins are what because when soldering 1/4" cables I just remember that "pin 2 is hot and 3 is not".
Now that all the technical mumbo jumbo is out of the way, to to from an 1/8" connection (like out of your computer or MP3 player) into the inputs on the amp, you will need a simple cable and a couple adapters. Get a "stereo 1/8" to two RCA" cable, and then two RCA to 1/4" adapters. That will get your left and right audio signal into the proper left and right connections on the amp. It is not possible to get balanced TRS inputs from a stereo 1/8" cable so the connection will use unbalanced TS connectors. The reason is because the 1/8" plug is using the tip and ring connections as left and right, and there are no more placesto get a balanced signal from. It is possible to change an unbalanced stereo signal into two balanced left and right signals if you use some transformers. But you dont really want to do that as there isnt really too much of a point. Unbalanced will be fine for most scenarios.
cable:
http://cgi.ebay.com/6-ft-1-8-3-5mm-m...3A1%7C294%3A50
Adapters:
http://cgi.ebay.com/RCA-Female-jack-...3A1%7C294%3A50