Check ebay for the comfort gel seals. Ebay.com rather than ebay.com.au gets better results. Or get them from Skylines.

I upgraded my DC 13.4's years ago but I was never really over the moon about them because when you fit the new speakers they are bigger and you have to remove some of the foam from the ear cups to get them to fit in, so if you have a flat 9v battery in your box (and no spare) then you literally can't wear them as it's too noisy (subject to aircraft type of course).

Thanks, & Wilco

Are the 13.4 shallower cups than some others, (like the 10-30s)?

I hope so.

I've got DC 10-40s and the Headsets Inc kit fitted unmodified. Part of the kit was gell-filled cups which made a big difference to the passive noise reduction.

They look and fit just like the original 10-40s, except for the box with the electronics attached to the cord.

I upgraded my 25 year old DC H10-30 headset several years ago with the Headsets Inc ANR kit. Initially I stayed with the original ear seals which were OK but last year I changed to the GEL seals from Skylines. I am now very pleased with the overall result and realise I should have done the ANR conversion years earlier. I also use rechargeable batteries and have had no issues with these (so far).