Complex sentence: Wagner had originally hoped the Parisian première would have taken place at the Théâtre Lyrique; however since the work was to be presented at the Paris Opéra the composer was required to insert a ballet into the score, according to the traditions of the house.
Split into simpler sentences: Wagner had originally hoped the Parisian première would take place at the Théâtre Lyrique. However, the première was at the Paris Opéra, so the composer had to insert a ballet into the score, according to the traditions of the house.