H264 with audio mapping options

Hello, I have a ProRes file with 8 audio channels. I have to encode an h264 from this and only consider audio tracks 1 & 2 as a stereo mix. I can't find any options with the "h264-Preset", with the "Quicktime-Preset" I can find the option to map the audio, but I have no option to select h264 as the codec. am i too stupid or is the media encoder just not able to create such a file?