Can I run Conventional and Post War with DCS ?

Yes you can - however, you have to be very careful because as soon as you turn on the power to the track with DCS it MAY be all the way up at 18 volts which will cause conventional locomotives to go really fast (had that happen a couple of times; fortunately I was able to grab the loco before if flew off the tracks!).

My instructions how to tun LEGACY on my DCS tracks contain the following step:

"3. Select the track and press the TZV hotkey (S2) to turn off the fixed track voltage to that variable track."

With the TIU connected through a variable channel, you can run conventional and DCS without changing any wiring between them.  What I do is set the TIU variable channels to fixed mode, that puts full voltage on the tracks.  So, I'm ready to run DCS command locomotives (or TMCC/Legacy, I have both).  I can use the DCS remote to select the track and change to variable operation by just turning down the voltage, then I'm ready to run conventional using the DCS remote.  A power cycle of the TIU returns the tracks to fixed mode.

I routinely run conventional equipment by using the variable output function of the docs.   Note that the min voltage is 5m volts.   This feature allows you walk around control even with old school Flyer and Marx.

Actually, you can program whatever minimum voltage you like with the TIU variable channels.  You can also program the maximum voltage for younger engineers.

You can program the minimum voltage in the remote but the wifi app from what I remember only starts at 5.0 volts which might be too much for some engines that use really low voltage. If someone has gotten around this then please let me know.

That seems like a major oversight in the app!

Well, I didn't know I could do that.  Time to dig out Barry's book again.