What's with the spaming?
Look just because it's in a Wiki doesn't make it correct. Wiki's are user modifiable.... I could easily go in there and post something that tells ya if ya hold your butt just right any sound system will be just like the bose.... but doesn't make it correct now does it? (that's a rhetorical question)
I know you mean well... but look at some facts:
1. Read the manual it specfies that the 1/4" input is designed for Hi-Z (high impedence) inputs... [editorial]it is not generally recomended to use unbalanced Hi-Z cables due to the potential of interference induced noise especially in longer than 3 meter cable runs.
I know you mean well. But, I have to go with my years of electronics training on this one. XLR is the best because it is a grounded and balanced cable providing me with the most noise reduction possible in my signal chain. I follow one rule: Your sound is only as good as the weakest link. (typically that's a cable).
Now back to the OP
Chuck, I think steve has posted may be the most ideal way for you to get a mono signal to the L1.