See we can categorise the directors in 2 ways
1) wholetime Directors/MD/Executive directors/full time directors engaged as employees
2)Part time directors/Non-Executive director
When we pay remuneration to the directors covered in category 1) then it is regarded as nevertheless Salary and hence TDS is deducted u/s 192 as TDS on Salary because they(directors) provide their services as the other employees of company do in normal circumstances.Thus service tax can not be leveid if TDS is done as TDS on Salary.
On the other hand, if payment is made to directors covered in category 2) above then it is regarded as providing services to the company concerned by the professional(director).In this case, directors render services in their professional capacity(not in the capacity of employees) and earn fees by way of sitting fees,commission or by way of any other name.Hence TDS is deducted u/s 194J @ 10% and not u/s 192.Thus, in this case services are provided to the company therefore service tax will be applicable.