Sorry- Accidentally posted on wrong account.
Phil
You can put sound and lighting into a dummy loco. It is actually much easier since there is room where the motor would have been in a powered loco. But to my knowledge the aftermarket QSI decoder isnt available. I think your best option would be a LOKsound decoder from ESU. You can order it loaded with any sounds from the library they have, and if you buy the programmer you can change the sounds later if you want. They may or may not have RSD-15 sounds, but if not you could find something close. At least for my money LOKsound decoders are significantly better than QSI.
I did see you want to be able to control it with a Quantum Engineer. This tells me you are running on DC? If thats the case I think you should convert over to DCC so you can fully utilize your sound decoders. LOKsound decoders will run on DC, but you are very limited as to the sounds and features compared to what you get with DCC. My reccomendation would be a Digitrax Zephyr. I bought mine for $150 a long time ago, I dont know what they cost now. The Zephyr is fully expandable and has most of the features of a more expensive DCC system. There are other systems that would also be good for about the same price like Lenz or maybe NCE. Digitrax best fit my needs but look at the others too. Whatever you do steer clear of MRC. The old prodigy works, but is extremely limited, The prodigy advance and express have more features but are anything but reliable.