Realtek audio setup

I recently built a new Desktop. Asus motherboard P8 B75-M/CSM, Intel B75 chip set. Running Windows 7.
I'm trying to set it up to make radio shows (podcasts). So, I bought a small mixer. Plugged the mixer line out into the BLUE jack on the PC (line in).
Problems!
1. The mixer audio appears on the PC speakers even when I have the Line In set to zero on the PC's mixer (software) panel. And when I turn up the input slider on the PC's software, I then get a mix of echoed audio and direct audio. Why?

2. This is really really annoying. If I right click the speaker icon and pop up the "Volume Mixer" it won't allow me to adjust speakers or system sounds or Line In, independently - the sliders all move together. This is madness.

Can anyone help? :cry

 

Go to Microphone in the Realtek HD Audio Manager in Control Panel, and make sure that in the Microphone Tab, that Noise Suppression & Acoustic Echo Cancel are on. Also when you right click on the Speaker Icon in the Taskbar, and Recording devices, that in Properties, that "Listen to this device" in Listen tab is not checked, and in Enhancements those settings you can play with to see if they make a difference. Make sure Immediate mode is checked in that tab.