You can grow your bacteria at temperatures as high as 65-70 C to count, however you can use Thermus agar which is resistant to higher temperatures.
It depends on which kind of thermophilic bacteria you have. If you have Thermus sp, Bacilli or other kind You should use different special Media, Nutrient Broth may be good alternative to use for Bacillus kind bacteria.
Well, choose an appropriate medium for your species and prepare it using thermus agar if you are welling to grow them at temperatures over 40 C. Be-careful, the moisture content in your incubator at high temperature should be monitored, thus you could avoid medium drying.