I own several MTH SD70ACe's, one SD70M-2, and several other MTH HO engines. All of my MTH engines are equipped with Protosound 3 and I run them with NCE DCC. They are smoothest running and best pulling engines I own. I have never had any problems programming or operating them with my NCE Power Pro system.
Early releases of the SD70's did not support advanced consisting, custom speed mapping, or function mapping in DCC. All newer released (since last February) do support these features in DCC. All MTH SD70's that were shipped without these features can have them added with a free software upgrade. Loading the updated software requires an MTH DCS system. If you decide to purchase one or more engines I'd recommend checking with your dealer to ensure the engine has the latest software update. Any reputable dealer should be able to upgrade the software for you before you buy.
The PS3 is one of the better sounding decoders on the market, and has BY FAR the best speed control. Every MTH locomotive comes out of the box speed mapped to operate in one scale mile per hour increments when your DCC system is set for 128 speed steps. Set the speed on your ProCab to 21 and the engine does 21 SMPH. This makes it extremely easy to consist MTH locomotives. You don't have to do any programing of CV's. Just build the consist and go. MTH uses an optical speed sensor on the flywheel to measure actual speed output. Currently, all other decoders on the market use BEMF to infer motor speed. BEMF works, but it is two orders of magnitude less accurate. You can always speed map other engines to run as close to the MTH speed map as possible. That's what I do with non-MTH engines. Others prefer to set their own speed curve. Until last winter, you couldn't program a custom speed map into an MTH engine. That has now changed. Any MTH HO diesel or electric engine can now be custom speed mapped.
Since you know you want sound and DCC I'd suggest buying the PS3's, rather than DCC ready. A PS3 locomotive will cost you about $225 street price. The going price on a DCC ready version is about $160. A Tsunami decoder and a coupler speakers from Tony's Train Exchange will cost you about $115 + shipping. If you go with the PS3 you can save yourself $50, save the time and hassle of installing the decoder, and have have superior speed control. You definitely get your monies worth with a PS3 engine.