Welcome to TT!
I'm not really sure what you should share with them. You could ask the ENT if he thinks the tinnitus could be attributed to the chronic headaches... I have no actual clue, but as a layman it would make sense to me.
Anyway, it's good you're getting your hearing checked.
And frankly, I hope your ENT isn't one of the morons who just say nothing can be done, learn to live with it. While that might often be true, that's so wrong to say anyway. It will be interesting to see if he mentions the terms habituation, tinnitus retraining therapy, sound enrichment, or anything worthwhile.
Let us know when you're back!
Fingers crossed everything goes well,
Markku