Well, I think I could go some way towards answering your questions.
1. I do believe this is already based on the GOG version.
2. Well, in the PC version, the pitch on the Tings does change just like in the other versions. It's just a much more bland sound overall. I don't know if it would be possible to get the PlayStation Ting sound into the PC version. I'll let the experts answer that!
3. That would involve changing the music in the middle of the level, which is more complicated that just changing what music plays in each level. I guess the "boss clear" theme from the PlayStation version could be put in fairly easily though, since the PC version already changes the music after a boss fight.
Also, just a hint: if you want to quote someone, use the quote button. It's the one with a giant quotation mark on it. If you do that, the person you're quoting gets a notification.