The fact that you can’t program new sounds into the Soundtraxx decoders doesn’t mean they sound bad.
I have never mentioned that Econami has an inferior sound - just that it is not as flexible or feature-rich as some of other sound decoders. I believe that I also mentioned earlier that it is the speaker and its enclosure (not the decoder itself) that has the greatest contribution to the sound quality.
Then there is also the capability of the audio circuitry. There are decoders with 8-bit and 16-bit audio channels, with various sampling rates, but IMO in N scale, where we use such small speakers and enclosures, the difference is not readily apparent to most ears. For example, a 16-bit decoder using high sampling rate with a poorly chosen speaker and no enclosure will not sound as good as a 8-bit decoder with a good speaker/enclosure combo.