Re-wiring the Sound for a Lionel Bandstand

First of all, i'd not worry about 'left' and 'right' speakers for  this arrangement.   There's not enough separation in that accessory to make it worth the effort.  Rather, I'd put in a decent sized single speaker compatible with your CD player.....or just use the one already there.   This is what I did for our store (LHS) HO layout, putting a single speaker just below the bandstand in the middle of the park scene.  

Then, make a new connector cable.....  Get a monaural mini jack/receptacle for the accessory end.  Get a stereo jack that fits your CD receptacle.  Simply wire both stereo speaker jack outputs to the common monaural jack terminal.  Plug and play!!!

We play a variety of band/orchestral discs.  The Christmas songs are especially popular in creating a seasonal mood in the trains department.  

As a side note, one of our employees does not like the two Christmas CD's featuring Alvin and the Chipmunks.  OTOH, we tell him that he needs to think about the singing differently.......it's really the HO folks in the scene!!

I have the same Lionel accessory.  It doesn't work, either.  I believe it's the cassette player drive belt.....they were notorious among cassette players sitting idle for years for drying out, taking a set, not doing their job anymore.  Of course, you can get replacement belts if you're so inclined.  But there are so many other player options....besides CD...nowadays that can be played through a simply modified accessory.  I plan to do the same......someday.   (Still down the bucket list quite a bit!)

FWIW, always...

KD

Depending on how tongue-in-cheek you want to go,  you could get a couple of Marshall Micro amps and, well... 

Alternately, you could build some more to-scale speakers and place them to either side of the bandshell.  Either way, no gutting of the shell would be required. 

Mitch