While reviews of older musical performances might be found in books, more recent performances are likely to be found in more current magazines and newspapers.
Consider the unique components of a musical performance that you might need to focus on:
For instance, if you search for a production of Turandot, you might find reviews from multiple performances... in multiple cities... over decades... with various artists.
Narrow your search slowly, using the most important components first, then adding less important ones as necessary.
Both databases have a similar look and feel, but the content they cover will be slightly different.
PQ Newsstream: major newspapers - mostly live performances
Music Periodicals: music industry
Finding information on contemporary singers will be more difficult than for those who are more established.
These individuals may still be making their mark on the music scene, and little may be written about them outside of performance reviews and web articles.
Putting together a biographical sketch of contemporary artists is very similar to finding performance reviews! Instead of beginning your search with the name of an opera, start with the performer's name!
You may still need to narrow your search with other identifiable information, such as voice part or a specific role to get on the right track.