Hi Anthony,
I don't think any keyboards are backward compatible as far as styles go ( except for the Yamahas who's styles are actually based on a midifile, and even then they're not 100% compatible because of the sounds themselves.
The quality of sound improves with each generation of keyboard and you also find that upmarket keyboards usually have better sounds than the lower priced ones, even though they may be using the same type of sounds ( Yamaha XG). For instance, I have a Roland VA7 (GS) and I also have a
Roland GS Sound Canvas module. When I play the same GS midifile on the Va7 it sounds far better than it does on the Sound Canvas yet they both have the same gs sounds.
Just say my old kn5 was actually had an nx sound source. I would hope that my new kn7 would sound better than a 5 or 6 year old kn5. So if the kn7 sounds better they've obviously had to change something. A sequence is still not going to sound exactly the same on the kn5 as it does on the kn7 even if it has NX.

I'm not sure I undestand the hassles you're having with the apc to smf convert?
Are you saving with Panel Header "On"
I would imagine in most cases you'd save a midifile as nx if you were going to share with kn7 users. The only time I'd save as GM would be to share with a non nx user. Then it would be up to them to tweak the sequence and find sounds that work.

Unfortunately that's the problem with most midifiles ( if not played on the original type of machine), they have to be tweaked , so they sound good on the machine you're planning to use them on.

Actually , there were far more hassles pre GM. I remember the days when synths all had their own sound & drum setups. At that stage you had just about no hope, if you wanted to play a song that had been created for a different manufactures synth. The drums didn't match, the sounds didn't match. Your song could be playing a bass drum instead of a hihat or a violin instead of a piano.

best wishes
Rikki