What is the fine-grained topic of the following text: Since that time, I have watched Pat expand his musical universe (and ours) with a seemingly-endless flow of beautiful and challenging compositions played on a collection of old and new instruments such as the Coral Sitar, the Roland GR-300 guitar synth, the Manzer Pikasso 42-string guitar, the Nashville-tuned baritone guitar, the Orchestrion and, of course, his 6-string electric and acoustic axes. Only return the topic.
Pat's musical evolution and use of various instruments