I think this discussion is beginning to point at the wrong culprit. SMF files on the net are made in many different ways. Some are made in real time on a synth, some are made in step time on a synth, some in step time on a computer, and all sorts of hybrids of these approaches. I have downloaded and played thousands of these from websites and from absm. Almost all of these play well whether I use my computer or by PSR-8000 to play them. In addition, so few absm members report problems with the files that they must be conforming to GM standards. Of course, some variation in sound must be expected. But if one a certain keyboard cannot play many Internet GM files it is probably due to a non-standard GM implementation. Then, why do the Tune 1000 files work on these synths. Because, as they have a financial interest in customer satisfaction, they listen to complaints by those people with synths that cannot handle the files. They make their files so that they do not run into problems in nonstandard, or at least unusual, GM implementations.

So, I would point my finger at General Music, absolve the Internet folks, and give credit to Tune1000 for accommodating General Music on General Midi.

But-this is just a FWIW opinion,