I would definitely replace it with a tsunami and remove the NCE. Soundtraxx has a replacement for it and also has a photo rich installation guide for your loco found here.
http://www.soundtraxx.com/documents/appnotes/SW1000&SW-1500App.pdf
http://www.soundtraxx.com/choose/step3.php?t=ho&s=Athearn
Springfield PA
The bad news, I had one of the sound only Digitrax decoders installed and thought it was neat until I installed a Soundtraxx unit. I shortly relegated that Digitrax to the pile of "I'm not sure what to do with it". Unfortunately the Soundtraxx decoder is not sound only. But if you go on their website and listen to them you will understand the difference in short order. The sound processor on Digitrax sound only wasn't good and I couldn't even tell if it was prototypical. Whereas the Soundtraxx does a good job in even getting the notching good. If you're looking for mainly horns/whistles and bells, the Digitrax would be fine.
I guess the good news is that there is decent sound out there to be had from those striving to be prototypical. QSI is coming out with a new decoder that could be as good if not better. They have a website where you can download the sound files and then listen to them.
Note that the speaker install is critical. You may want to check out the Soundtraxx installation manual to get some ideas on speaker installs.
Richard
The NCE motor decoder doesn;t HAVE to stay. You'd be better off, particualrly in a smaller loco like that, to repalce the motor only decoder with one that does sound and motor control, such as a SOundtraxx, QSI, or ESU.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
I am thinking about installing an add-on sound decoder to an Athearn HO SW1500. I already have a NCE decoder installed in it, so it must be able to work with it. I looked around and it looked like only Digitrax and MRC made sound only decoders. I have read that the sound quality of the MRC decoders is not great, so I want to stay away from them if I can. Does anyone have digitrax sound installed in one of their engines and can tell me how good it is? Also, are there any other manufactures of sound only decoders?
thanks, sfb