Talking of wine from Korat province, think the winery/wineries
Lomuamart is refering to are in/around Khao Yai, they are all like farm resorts with an appropiate price tag attached to them(resort and wine), expensive if I remember correctly, 3000-5000 baht a night at a conservative estimate.
Think there is one at Chok Chai Farm aswell, think there is the right type of soil in these areas, which is very dark as opposed to the red coloured soil(full of iron oxide).
Agree about Chateau de Loei being good, the best is obviously a personal taste but in general Thai wine is getting better all the time.