I bought a quad for my Prima-Luna Dialogue 5 power amp. With 70 hour on them they sound wonderful. I understand they need 150-300 hours and yes the sound has changed dramatically since new. From top to bottom more musical with more resolution and emotion. The bass goes deep with power and accuracy. The top end is extended with out being bright. The mids are sweet and warm. Separation of instruments has been overwhelming and has been a huge, dramatic improvement. Without any doubt this is my best audio upgrade in years. Highly recommended!