2 rail sound

Ironically, MTH's command kits (Proto-2 and [soon] Proto-3) operate in conventional mode with sound and will operate under conventional DC. I'd wait for the Proto-3 kits as they'll reportedly contain the DCC decoder as well and won't have polarity issues with respect to command operation.

Hope this helps. I'm sure some of my colleagues will chime in.

My recommendation is to think again about DCC.  With it comes smoother running, easier wiring, multi train operation (without flipping block selectors), constant lighting, and a wide and growing selection of sound decoders.  Yes you'll have to pick one brand for the base units and throttles (NCE was my choice), but you'll have complete brand independence for decoders you can mix and match to the need.  MTH, AtlasO, and Sunset diesels are now ready to roll with DCC compatible sound.  At least 4 brands of decoders are available for retrofit in older steam and diesel locomotives.

Ed Rappe