Kev, reading your post took me back 6 years to the 10 hours I spent in the tiger moth at the tiger club. I couldn't believe the ringing in my ears after 20 minutes.
I was advised to go to headset service and get an old fashioned leather flying hat. Properly fitting earcups solved the issue immediately - no more tinnitus. Cost was about 220gbp. Money well spent. (Still could not believe how much spit came out of the mouth piece after flying) .
In my day you had to get a dynamic microphone, but chuffer seems to be saying elecret is the thing now. Enjoy the mighty tiger.
Its interesting to reflect they used these headsets until the early meteor days.