Ask the user which sound card he wants to have as default

After installing Ubuntu on a machine that has more than one sound card, it can appear that the sound is not working.
The reason is that the speakers of the machine are connected to the sound card that is not the default one.
The user can then think the sound does not work with Ubuntu on his machine (as happened to me).

During the install, it would be good if Ubuntu detects that there are more than one sound card and then asks the user which one he wants to use by default.

For the live CD a pop up window could be shown to the user.

Here is a 'mock up' of what could be shown to the user:

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<!> You have more than one sound card installed in the machine, which one would you like to use by default?

(Drop down menu:)
1 - VIA4564 -
2 - SB Live 5.1 -
(external sound card should be selected by default)

//Note: You will be able to change this later in the menu: System > Preferences > Sound.//

<Ok>
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