The Vaughan Williams / Thomas Tallis piece is beautiful, start to
finish. Those voices work well together. Choir in place of the
string section may have worked nicely too.
http://www.mikedickson.org.uk/mellotronworks/Quite complex 3/4 of the way through.
There's a Richard Wagner piece that would suit 'tron voices well like
this. I'll try to find it.