youtube will always transcode that to aac.
And vorbis. And opus. And you don't know which encoding or bitrate the viewer will get.
Chiptunes are a particularly bad match to any lossy codec at all; with some I can pass an ABX test even at bitrates well above the nominal "normal" audio "transparency" bitrate. The only conclusion I can come to, since you can't specify the codec, is to just not worry about it much.
It's still a GIGO rule. If you are wanting to make sure that the listener gets the highest fidelity audio, you have to upload it in PCM and and have the video at 720p (as I've stated several times already) otherwise Youtube will force the audio quality down.
I always find 240 video/audio (that gets converted to 360 by youtube) is extremely terrible, like the audio has been resampled to 16khz.