The Atlas Gold series were (for me) GREAT locos. I still own 2 of the FM Trainmasters and other than dirty wheel problems, they still work and sound great.
Tony's carried the original speakers and they will work fine as replacements. I have also replaced some of the original speakers, in other locos, with small sugar cube speakers with surprising results. "Bass" response with the small enclosures is remarkable compared to the "compact" speakers available when these locos were released almost 20 years ago. Don't be afraid to try them . Modifications in mounting them is needed but they do work well.
As Paul mentioned, the original decoders were the "crippled" versions thanks to Mike's Train House's frivolous lawsuit back then. After the suit was dismissed, the upgrade chips and programmer were released. The old chips had a LOT of problems like no BEMF, loss of programming after a short circuit, running away after a short circuit, and more than can be addressed in this forum.The $30.00 price for the upgrade is well worth the investment. It also provides a way to upgrade the sound file if you own the QSI programmer or know someone that does.