"My time with the orchestra was a turning point for me and made me realise that I wanted to make music my profession," says the violinist, who has toured the world with the girl group Bond.
The quartet - a potent mix of sex-appeal and classical-inspired pop music - has sold millions of albums. That success traces back to her three years (1992-94) with the orchestra, she says.
"Elgar Howarth was the conductor when I joined the NYOW and he was inspirational," says Eos, who comes from Cardiff.
"He had a great commitment to contemporary musicians so we performed a lot of modern music.
"I remember one work we did which was a cacophony of sound, including an air raid siren. It was very exciting and taught me how you can break the rules and also reach the audience."
Eos, 30, who first picked up a violin aged five and later trained at the Royal College of Music, adds: "I'd been a member of school orchestras but with NYOW we were treated as adults."
Her sister Tanwen was also a member. A violinist and French horn player, she is now a music teacher in Cardiff.
Eminent composer Dr Alun Hoddinott was a 16-year-old violinist in 1945 when he became a founder member of the NYOW.
Its first conductor, Clarence Raybould, helped Dr Hoddinott make the decision to focus on writing music rather than playing it.
"He looked at my early compositions and helped me enormously," says the former head of music at University College, Cardiff.
"I went in as a violinist and went on to the viola, but it wasn't long before I had to make the choice between writing and playing music. It was an inspiring time, working and talking with experienced musicians who came up from London to tutor us.
"The previous years had been very hard with the war. This was a starburst of creativity and optimism."
Being a member of the orchestra in the 1970s taught politician Edwina Hart, AM for the Gower, all about equality.
"I was an only child and not used to sharing anything," says the minister for social justice and regeneration.
"You can't always be the loudest viola player, you have to fit in. That lesson served me well when working with the trade unions."