Apple TV remote

What is your model Apple TV? Identify your Apple TV model - Apple Support

What is your model remote? Identify your Apple TV remote - Apple Support

Speech is supported for Apple TV (4th generation or later), not earlier models.

Use Siri on your Apple TV - Apple Support

Use Siri dictation on Apple TV - Apple Support

Also, you interface language must match the supported languages for your region.

Here's where you can use Siri

Siri is currently available on Apple TV 4K and Apple TV HD in these countries, regions, and languages: Australia (English), Brazil (Portuguese), Canada (English, French), France (French), Germany (German), Japan (Japanese), Mexico (Spanish), Netherlands (Dutch), Norway (Norwegian Bokmål), Spain (Spanish), Sweden (Swedish), UK (English), US (English, Spanish).* 

The microphone is at the top of the Siri Remote.

The only configurability is in Settings﹥General﹥[sɪʀɪ] (options 8–11), and is basically on On|Off switch and a language selector, if there is more than one language supported for your region.

Other microphones are not supported (except for the mic on an iOS device when configured for use as remote, and possibly any remote solutions provided by home automation specialists such as Crestron, Savant, Control4).