How to monitor the audio that's selected as the input to VidBlasterX's Modules
If you're using Windows 7 or higher, you should be aware that audio recording device inputs are not necessarily routed to the playback output for monitoring via the PC's default speaker/headphone outputs. Sometimes this routing is added in the application software, and sometimes not (to avoid feedback if a mic input & speaker output are both live). If you wish to monitor audio in this way, but are not hearing anything coming through the speakers/headphones, have a look at the particular audio Recording Device properties that you're using for VidBlasterX's input (in the Windows Control Panel) and, under the "Listen" tab, tick the box "Listen to this device" if it is not already selected. Then, in the same dialogue box, you should be able to choose to have it play through the default playback device, or explicitly be able to choose the HDMI audio output (when connected and active). When using the default device, an extra volume slider control will appear in the Windows Playback Volume Mixer for you to adjust the monitoring volume relative to other internal sources.
There is a caveat to this, which can occur if you're using Player modules. If the sound from a Player module is being output from the default audio device, being fed to an external mixer along with various microphone inputs, and the output of the mixer is being fed back into VidBlasterX's Recorder or Streamer Modules, then "Listening to that device" will send the signal back out to the mixer and could cause an echo or "howlround" feedback, or at best some colouration of the audio from the Player. To avoid this, either an extra soundcard or USB audio device should be used so that the Player can be set to use a different audio output device to the one that's being used for overall monitoring, or instead of using the Listen to this device option on the PC's audio input, the speakers or headphones should be physically connected to the mixer rather than the PC. Most mixers will have an output for this purpose (eg Control Room o/p), on which the volume can be controlled independantly of the main mixer output.
Speakers property settings in Windows 7
There is another way in which sound from the Mic & Line inputs can end up being fed through to the output. In the Windows 7 Control Panel section for Sound devices, under the Playback tab, you can find the settings for "Speakers" - in effect the Line Out connection. In the Speakers Properties section, under the Levels tab, are various level controls equivalent to the "Playback Mixer" volume controls found in Windows XP and previous operating systems. As well as the Speakers volume control (effectively the main Master Output level control), are level controls for the inputs (eg Line & Mic) together with Mute controls (ringed in red in the picture, left).
If you are getting sound from the input being fed through to the output when you don't want it, possibly causing feedback as described above, make sure this control is in the Mute position (showing a red stop-sign next to the speaker icon for that input).
If you do want to monitor the audio that's going in to the Line Input, by having it routed through to the Speakers, then enabling the Line In on this settings panel will do that, and is an alternate to setting the "Listen to this device" option in the Line In properties. However, it is not as versatile as using the routing on the Line In panel, which can send the signal to any connected audio device, including embedding it in the HDMI or SDI output of a graphics card or Blackmagic card. In the Speakers panel, the Line In option always relates to the input of the same device, and cannot be used to select the Line In from a different device.