This was posted by someone else on another message board:
(Season 6)
'On the main menu, highlight the "once more with feeling" episode and press enter. From that episodes menu, select 'Language selection' Once in the language menu, hightlight the resume episode and press up. A little Buffy logo should appear.Press enter and you will be shown a two minute clip of some cd soundtrack signings.
The second one is on disc 4. Choose any episode and press enter. Again go to the 'language selection' menu for that episode you choose. As before, just highligh 'resume episode' and press up. The logo should appear again and press enter. This will tell you how to access the call sheet on your pc.'
OR...if you have the Region One disc (because that was for Region Two) then:
'For Season Six, on the second disc, go into Once More With Feeling and go into the language menu. Highlight English for the Hearing Impaired (Or something like that) under the captions subtitle and press the left button on your remote. This will highlight the hidden "B". Press enter / OK and you will access the CD signing for the Once More With Feeling Soundtrack'
Hope that helped a bit...