Meaning no disrespect to you, but your sources are wrong. The following is on the home page of idononfox.com:
Now, we look forward to the Top 11 Finalists tackling the songs of the ‘50s, Tuesday, starting at 8/7c. Then, on Wednesday, starting at 9/8c, come back for the results and a very special live performance by the legendary Barry Manilow.
Manilow will perform next week, but the theme for the week is songs of the 1950's.
They are going to Vegas this weekend to work with him is what I am now told. Since he has a cover album of 50's songs that's probably the angle.
It appears that the show will have artists involved with different episodes.