What is the correct way using SX4Pt, to Mix in Mono?
Toggle mono interleave on the Master bus is what is currently being used.
Per Track Interleave = different sounding result
MASTER> Channel-tools Kill Center = different sounding result

*SX4Pt = SONAR Platinum
SX1
SX2
SX3
SPt = WTF?

If your objective is a mono final mix, then every track should be mono, every track's interleave should be mono, all busses including the master should be mono, and you should only use mono effects. Of these, only the mono interleave on the master bus is technically necessary, but placing any stereo elements prior to the final bus may cause difficult-to-troubleshoot problems.

Hi. I used the Master interleave button until I got a monitor controller with mono / stereo button. I think that is "the right way" to do it. Other will know better.
All the best.

I add "Channel Tool" to the final bus and use that to hear mono

I add "Channel Tool" to the final bus and use that to hear mono

@bitflipper final mix is not intended mono. I'm attempting to mix in mono using EQ and panning, then final to stereo.
@magik570 What setting is used? When I used channel Tools it choked down all the audio too low, it sounds way different than using the interleave button on the Master.