Does your Bachmann 2-8-0 have a 8 pin plug inside? If it does, there should be a little rectangle, which is the cap or cover for the plug. Gently pull the cap off, and you will see 8 pins in 2 rows, with 4 pins on each side. Now, get a N scale or z scale decoder (I used to own a Bachmann Spectrum 2-8-0, so I know how small the tender is, so I would get a Z scale decoder.), with an 8 pin plug, if you don't want to do and soldering. Now, for sound, get a Sountraxx Tsunami Micro 750. It should fit, but no 8 pin plug, so you would have to do some soldering. The Tsunami has sound and DCC, so all you would is a very tiny speaker. Then you will have to drill holes in the coal load ( very small holes) so the sound will come out. Then you will have to either buy a small enought speaker baffle for the speaker, or glue it on. Then solder the wires that come from the sound decoder, that go to the speaker, on the speaker. The instructions should tell you which wires goes where.
Hope this helps.
- Luke
Modeling the Southern Pacific in the 1960's-1980's