1) How many channels does TAK support?
The stream format supports up to 16 channels.
But the current codec implementation only supports up to 6.
Reasons:
I didn't have files with more channels to test and tune the codec. Furthermore this tuning is quite time consuming for multi channel files. Especially because TAK's stronger presets try to apply TAK's channel decorrelation filters ("joint stereo") to any possible channel combination.