These flowers are absolutely stunning.

I don't grow such species but am always fascinated by their flowers. Furthermore I read they would be hard to grow. When I read your growing advice I'm wondering how you get the peat wet again after such a stong dry period? Do you always repot before the growing season starts?
For sure it is very difficult and long to get the peat wet again after such a long rest period, and it is the main reason why I would like to change their substrate next season. Moreover, when the peat is finally wet again, I am always afraid that the tubers will rot. So I will try akadama and kanuma.
I haven't cultivated this genus for very long: I have had my oldest Thelymitra for only 2 years, so I haven't repotted them yet. They have always remained in their pot during their rest period. As already said, when they have all gone dormant within a few weeks, I will repot them in a substrate made of kanuma and akadama. Then I plan to repot them every 2 or 3 years.
You should give a try to this genus, and the only seller I know in Europe is one of your compatriots. ;-)