Yellow "TX" button in DAX

You need to turn on DAX for transmit:

That is part of your Mic Profile. I have the following mic profiles (just to give you an idea of what you can do):

Len CM500 - for my Yamaha CM500 headset
Len FHM-3 - for the stock hand-mic that came with my rig
LenDigital - for VarAC (DAX on)
Len HM-12 - for my Heil mic (PROC on)
Len HM-12 FM - for my Heil mic when I operate FM (PROC off)
Len Laptop - for my laptop mic when I am operating remotely

Go to Profile Manager and select the Microphone tab. There you will be able to create any Mic Profiles that you want. When you have a profile selected, any changes you make to the mic characteristics (DAX, PROC, MON, Mic Level, etc.) and TX equalizer will be automatically saved unless you turn off auto-save.

As far as VarAC goes, in the VARA HF settings, choose these DAX input and output devices:

In VarAC Settings, Rig Control and VARA Configuration, select SmartSDR for PTT and Frequency Control. Select TCP for CAT Configuration and the values I show below for Host and Port.

There are probably other things that I am not thinking of, but that should get you started.