Have you tried using the little yellow foam earplugs under the Telex? That seems to work best for me, but I've never spent much time in a 737. From what I'm reading here, it requires a full on noise cancelling headset!

The DC's are just too hot and heavy for me, oh, and I don't like sharing a microphone with everyone who's worn it before me. I've seen where some of those mouths eat!