System default (preferred) device issues
Why system default device may be arbitrarily changed
Please note that your system default audio device can be changed in result of VAC installation if you had not previously assigned this device explicitly. If a default device was assigned explicitly, it remains unchanged. If it wasn't, Windows may use any of present devices, and there is no easy way to predict which device will be used. VAC installer itself never changes default device settings; it may be done by Windows if default device wasn't set explicitly.
To set a default device, open Audio Properties applet. Then find a property page (tab) that displays Playback and Recording settings and select particular devices from the lists.
Note you must always select each device from a list and click OK or Apply, even the selection already shows this device. Windows creates default device registry record only if the device is set explicitly. If a device record is not present, Windows picks a device by its own rules and displays it in Audio Properties page. If you will install/uninstall another audio device, Windows may pick some other device in the future.
Using a Virtual Cable as a system default device
If playing and/or recording application does not allow to specify a recording/playback device directly, try to set Virtual Cable N as a system default device (Wave Mapper) using Audio Properties Applet.
Keep in mind that a system default playback device is used by Windows to play system event sounds when you open/close a menu, run/exit an application, when message boxes appear on the screen. If you set a system default playback device to the Virtual Cable, these sounds are directed to this cable. You will not hear them but they will be passed via the Virtual Cable to its recording clients. If you don't want these sounds to be passed via the Virtual Cable, disable them in the Sounds tab by setting a sound scheme to "No sounds". You will be prompted to save a current scheme to re-enable it in the future.
Some poorly designed applications always use a first available device and cannot be configured at all. In Windows 2000, to ensure that Virtual Cable 1 is a first device, you should disable all other audio devices. Don't remove audio cards or uninstall their drivers, just disable their functions in the Device Manager. This may allow you to achieve your goal but you would not hear any sound until you re-enable hardware audio.
In Windows 5.x, default audio device is set at per-user basis so you can assign
different Virtual Cable devices as default devices for different user
all applications started under a certain account, default
recording/playback devices will be mapped to appropriate Virtual Cables.
In Windows 6.x, default devices are set at per-system basis so you cannot use this technique.
To create additional user accounts at your computer, log in to the Administrator account, open the "User accounts" applet in Windows Control Panel and create one or more user accounts. If you usually work under a limited (non-administrative) account, create limited accounts too, otherwise create administrative accounts because not all applications, especially old, can work properly under a limited account. Once each account is created, set a password for it.
Another way to manage user accounts is using Administrative Tools - Computer Management item in Windows Control Panel. User accounts can be controlled in User Accounts and Groups - Users item. Creating a new account, specify a password, uncheck "User must change password at next logon" and check "Password never expires".
Once additional accounts are created, log in under them using Fast User Switching feature or logoff/logon sequence, and set different Virtual Cable devices as playback and/or recording devices, as needed.
To start an application under a given account, use "Run as..." item from a shortcut context menu. Open the Start Menu, locate application shortcut as usual, but use right-click instead of left-click. A context menu will appear. Left-click at "Run as..." item, select "The following user" and enter account name and password. If both were entered correctly, application will be started under given account and use different preferences than it uses under your usual working account.
To start applications automatically from a command (batch) file, use the runas command. See Windows Help and Support for details.
To avoid unneeded complexity, use additional accounts only for applications that don't allow to select any available audio device and use only a default one.
Please note that each user account has its own preferences: desktop themes, sound settings, application working directories, temporary files etc. For example, if an application uses a working directory, creating project files in it, such directory may be different under different user accounts. So you may need to specify these preferences manually if the application works under an account different from your usual working account.