ant1 wrote:you should not mix with simple Y splitters like this. it is designed for splitting not for mixing. it may work in some cases but it is a pretty bad idea
"Anything that can be hooked-up wrong, will be. You-know-who said that, and she was right. A wye-connector used to split a signal into two lines is being used properly; a wye-connector used to mix two signals into one is being abused and may even damage the equipment involved.
Here is the rule: Outputs are low impedance and must only be connected to high impedance inputs -- never, never tie two outputs directly together -- never. If you do, then each output tries to drive the very low impedance of the other, forcing both outputs into current-limit and possible damage. As a minimum, severe signal loss results."
Whoops your a bit too late, I literally just got done soldered my own Y cable.
Too my surprise it seems to be working quite swimmingly.
What/Who are you quoting?
www.rane.com/pdf/ranenotes/Why_Not_Wye.pdf
i also saw some on wikipedia about it but i can't find it any more. i do not really understand electronics myself i am just passing on what i have heard
if it works for you then carry on i gues? 
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edit: supposedly you can turn this into a basic passive mixer just by adding two resistors. if you are a dab hand at soldering maybe that will be no problem for you. i don't know what values you'd have to use though