I saw today's episode and noticed you were trying to get Virtual Audio Cables to work, but I'm guessing it didn't work out because you ended up using the mic-record-speaker's-sound method.
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I think how you would want to do it is this
Mic -> Line 1
StarCraft II -> Line 2
Line 2 -> Line 1
Line 2 -> Speakers
Line 1 -> Stream
http://img442.imageshack.us/img442/5959/flowchart.png------------------------------------------
To get more lines with VAC, you go to the Virtual Audio Cable's Control Pannel.
Start -> Programs -> Virtual Audio Cable -> Control Panel
On the top left you will see Driver parameters. Set cables to 2 (or more if you have a different flowchart of sound that uses more than 2 lines) and click set.
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To route the sounds like the flowchart, launch Virtual Audio Cable's Repeater.
Start -> Programs -> Virtual Audio Cable -> Audio Repeater
I suggest making a shortcut to this because I don't know how to make it automatically start.
Here's a screenshot of how I set it up.
http://img10.imageshack.us/img10/6433/vacrf.png------------------------------------------
In StarCraft II, just set your sound to Line 2.
I'm not sure what you are using to stream, but I am using Adobe Media Live Encoder and in that I just set the Audio Device to Line 1. So just whatever you're using set that as the input device.
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Lastly, we have Line 2 to Speakers.
I think this method is only in Vista and Win7, so if you don't have either, use Audio Repeater to route Line2 to Speakers.
Start -> Control Panel -> Hardware and Sound -> Sound
Go to the "Recording" Tab, scroll down to Line 2, and click on Properties.
In Line 2 Properties, go to the "Listen" tab, check "Listen to this device," change "Playback through this device:" to your speakers, and click Apply.
Here's a screenshot of that last part.
http://img143.imageshack.us/img143/6751/line2c.png