You can't use m-track for DC as the two rails are electrically joined to the metal track base... This means that if you were able to connect to each rail it would simply short out.. It should be possible to use C-track for DC, but you need to do lots of work - it would be much easier to just have a separate DC line made from suitable (and cheaper) track..

C Track can be used for AC and DC, providing that the contacts which link the two rails together on each track section are severed, resulting in separate circuits for each track. Once that is done, it should be possible to run DC trains on the track. K Track is designed with separated tracks. The only place where the rails are connected to each other are the power supply tracks, switches and contact tracks. The power must be connected to the rails by soldering a wire directly to the rails, as the track section with contacts cannot be used.

I would probably recommend using C Track radius 4 and 5 for AC and setting up a Trix C Track radius 3 DC track alongside. This may pose an issue if you wish to have AC tracks on the inside of the layout (ie siding). This can be solved by having the AC tracks inclined on one side of the layout and the DC Tracks declining, so that your siding passes over the DC tracks on it's way to the inside of the layout.

You can use DC electrics on AC track if you equip the catenary with DC power. This solution cannot be used for steam or diesel loks.

Regards

Mike C