I only heard Segerstam's M6th and M9th. I recall that the Sixth, which was the first in the cycle, had a badly tuned timpani in the Scherzo. The whole performance moved forward clumsily and pointlessly without any strong argument that goes with it. I gave it away eventually. As for the Ninth, the playing and sound improve markedly but the slow, crawling tempos rob energy and impetus of the music. Still, it's a keeper for those who are searching for a radical approach to the symphony.
John,