It does not.
Even though the channel 3 EQ only has the lower frequency knobs, it does not mean it can only accept a low pass signal, OR that it only outputs a low pass signal.
You can send a full frequency signal to channel 3, it will accept and pass thru whatever you send it.
The reason why there is only the low frequency controls on channel 3 is because 9 times out of 10 it will be used for a sub channel output.
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