John, Protosound 3 upgrade kits are available from MTH. A lot has to be changed out besides the boards. That includes, electro-couplers, leds, speaker, wiring harness. The kits come with everything and detailed instructions. I have done them for my own engine. Last I checked they are $199, with a discount if you join the MTH Club. Many folks on the Forum and other certified MTH technicians will do them for a charge. As you can see, it isn't an investment to be taken lightly. I think you need to decide if the engine is worth the cost to upgrade versus buying another engine and selling the current one to a conventional operator.
Case in point. I bought a Protosound Western Maryland BL2 and upgrade kit thinking MTH would never produce such an oddball again in the foreseeable future. No sooner had I completed my upgrade, MTH announced a PS3 BL2 in Western Maryland colors. I saw the new product and it is better detailed for about the same cost I have in the one I upgraded. 
If I had paid someone to do the upgrade, I would have had more money in the less detailed upgrade than I would have had in a new one. It was an experience.
I would say some of the experts will chime in with details.
