A little audio class 101.
Windows considers a line to be a single audio output. In order to have stereo you need TWO lines. Lines in this respect should not be confused with line as in Line-In on mixers/controllers. A Line-In input refers to a line-level (as opposed to a microphone signal which is MUCH weaker) input on a mixer and the term is used for both stereo inputs (mostly on DJ related gear) as well as mono line inputs (like live sound and studio mixers0.
You are looking for a 4-channel solution, which requires 4 stereo outputs. This -in windows terms- 8 lines.
Windows correctly shows the MC4000 built-in sound card as line 1/2 (channel A) and 3/4 (channel B).
The MC4000 is a dual channel/dual deck controller, designed to give you two deck control with a fader for each of the two decks. Some controllers will have dual channel/four deck control, meaning you can switch the controls for deck 1/3 and 2/4 by pressing a button. But both decks would share a single fader for 1/3 and a single fader for 2/4. Finally you have four channel/four deck controllers. Here you can also switch controls between decks 1/3 and 2/4 but each will have it’s own fader.
Essentially you have the wrong tool for what you are trying to achieve. While an excellent controller, the MC4000 just not have the features that you need to perform the way you describe.
Several scenario’s are possible of course:
- Get DJ software that has karoake option built-in. Effectively every software with video option should do, right? Which means the video plug-in of Serato, VDJ has video option I think, I know Cross has it in the full version and probably others. That way you can just be a two deck DJ with your MC4000, route your video to the screens and work that way
- You can get an extra sound card and pipe your karaoke output to two channels on that external sound card. You’d need a small PA/DJ mixer for example that can handle 3 stereo line inputs (one for the master sound from your controller and one each for the stereo karaoke channels). You,d set and forget the level fader for the controller as you’d be using the faders and master volume on the controller for that and use the karoake faders on the mixer for those two channels. This would give you full control over 4 channels.
- You can consider moving to a 4-channel/4-deck controller (preferably with stand-alone mixer capability) in which case you can either use option 1 (DJ software with video - The MC6000 even has a switch to set your cross-fader to video mixing) or option two (but without an extra DJ/PA mixer).
Hope that helps a bit.
Just my two cents as usual.