using the mth z 4000 with the dcs remote system

Basically, your thinking is correct.  While you can power the TIU using the fixed1 input, I use a wall wart that way the TIU is always powered but, I also use Legacy and, occasionally, conventional trains.  For DCS all you need is the Z4000 and the TIU.  Also, you do not need 20 volts, 18 is plenty.

Greg,

Am i thinking correctly ?

Yes, however, as Dan posted above, try 18 volts rather than 20 volts.

Also do i need to have a power source connected to the tiu at the auxiallry power connection using for example a Z1000 power brick ?

No, however, it's better to do so if you ever plan to use more than 1 TIU channel to run trains. Otherwise, any time power to Fixed #1 is lost (fuse blows, etc.), all TIU channels will lose the DCS signal.

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 MTH's web store!

thanks for the info guys !