Complex sentence: The origin for the recordings were made in 1998 when Berglund conducted the Chamber Orchestra of Europe at the Edinburgh Festival in a complete cycle of the Sibelius symphonies, which was notable for using smaller string forces than usual in some of the symphonies.
Split into simpler sentences: The origin for the Sibelius recordings were made in 1998 when Berglund conducted the orchestra at the Edinburgh Festival in a complete cycle of the Sibelius symphonies. What was especially notable was using smaller string forces than usual in some of the symphonies.