We have DC H10-56HXL for the BK and 206's, and use Bose X's in the 109E. The Bose are excellent in the quieter cabin (standard fit, wired in and not changeable), but poor interface with the Agusta audio system, resulting in low volume. They are also designed to be worn only "one way" (left & right earpieces), which doesn't always match the pilot's preference (instructors always seem to want the mike boom on the wrong side, which puts the headband and earpieces misaligned to normal ears).
The 56HXL are very quiet and comfortable, although a bit bulky. Typical David Clark, very well built and robust, good battery life, but mine has an annoying "beat" in the right ear until airborne in the BK. The ear seal is sensitive to noise coming in via the disruption caused by wearing glasses, but this can be minimised by fitting David Clark's foam pads to the arms on the glasses. I suspect that the BK117 beat is from rotor downwash flexing the pilot's window: I can stop it by hand pressure on the perspex, but it would be better if it didn't happen in the first place!
We have had ENC kits on order for our Alpha helmets for 4 months, when (if?) they arrive, I'll let you know
