Fixed and Variable on same loop?

I would just use the variable channel set to fixed for PS2/3 and go back to variable for PS engines.

Basil,

Can I connect both the fixed output from the TIU and the variable output to the same loop of track to run my non-DCS power?

Just connect power (it can be the same power source or two different sources)  to both Fixed #1 and Variable #1. However, only connect Variable #1 to the tracks. Then, you can control the PS1 engines with the TR screen on the DCS Remote and also control PS2 or PS3 engines on the same loop using the DCS Remote's ENG screen.

Or should I just buy the Z4k remote receiver and run the PS1s with that?

If you have no PS2 or PS3 engines and a Z4000 transformer, that will also work.

have you noticed is selling for $500 - 1200 on Amazon?  

I'd suggest that you purchase the book through OGR at a considerably lower price!  

I forgot to mention I have the Z4000 transformer (I guess that's implied from the remote question, though) and one PS2 and one PS3 currently.  And I'm looking to upgrade my Soo SD40-2 from PS 1 to 2 or 3, so I'll be down to one PS1, in the near future,  hopefully. 

Basil,

In that case, you'd be best off with my first suggestion.

However, if you were to purchase a Z4000 Remote Commander receiver (only), you could use it to control the Z4000 from the DCS Remote directly, via DCS Z4K Tracks. However, that's a different discussion. When you get a copy of The DCS Companion, you can read all about how to do that, along with the advantages of doing so.

This and a whole lot more is all in “The DCS Companion 3rd Edition!" This book is available from many fine OGR advertisers and forum sponsors, or as an eBook or a printed book at OGR’s web store!

If you set the Var channel to Fixed mode it's going to power up with full track voltage every time you turn on the layout.

I would set the var channel to var mode and  then scroll up the voltage  Using the TR command... for conventional running. 

For command really scroll up the voltage and then select the ENG command (green ) on the remote.

And The tiu need a power supply to function... power to fixed 1 or an aux power supply.