Hey. I saw this post ages back and can't remember if I replied or not :/
I also read through the Minecraft Forums one and saw that you needed software that could seamlessly switch between music and a mic input. Instead of using software for this, you would be much better off (Much much better off) using a mixer.
They can be quite cheap ($50 for a cheap one, $100 for a nice one)
Some even have a USB Audio interface in them so you can just plug it in directly to your pc and send sound/music out to it and receive it from it.
I reccomend the Behringer Xenyx Q1002 as it has two XLR inputs (For mics), full band EQ (For getting rid of hiss and hum and feedback), it's fairly small, it has 6 quarter inch inputs, one phono out which is great for small recorders, and will act as a soundcard for your pc, so all the audio comes in on the same channel and can easily be streamed using any software.
It would also be good if you had a seperate audio interface with quarter inch out to connect into one of the channels. This way, you can setup your music playing software to send sound to that, and it would be easy to adjust the volume.
