More 4 channel audio for broadcast ?

I am so close to outputting 4 channels to tape, but need a little more help.

For reference Network requires.
Full stereo mix including music/Fx on 1/2
Mono mix of Vo/Nats/Sot on 3
Mono Music on 4


So I have set up my 4 channel outputs in the sequence>audio output and this is working.

1 & 2 are set for stereo
3 & 4 for mono

I understand how to assign each timeline track to an output also. My question now is about mixing down in the time line. Right now I am using a1/a2 for vo/sot a3/a4/a5/a6 for stereo music, a7/a8 for FX. Do I need to mix these down to a1/a2 to output ? I have tried to nest "with mixdown" selected all the audio but when I do, it is creating audio on a1 thru a4, I removed a3/a4 and it still sounds fine, but is this right. Once I get this mixed, I then copy and paste my original audio to unused tracks and assign these lower tracks to 3 or 4 as required.

Is this the best way of doing it ? Cheers