Over the past couple of days, I've been working on Sound Manager, which was intended to be a personal use replacement for sound_pool. I intended to release this to the public for potential expansion/inclusion in the NVGT engine itself once it was more mature. I'm happy to say that I've got this running a couple of games now and barring a few little issues mainly to do with rotation, because I have no idea what I'm doing, it's ready for public consumption. There isn't any documentation yet, so you'll have to examine the code and class functions to figure out how to use it for the moment. Hopefully if it becomes more popular, people will create examples and docs for it. Enjoy!
Also what exactly are the rotation problems? Haven't faced any yet. That either seems to be a problem of the rotation.nvgt thing. Seems to be quite old.
As of this current moment, I do not have plans to add behind_pitch_decrease, but perhaps some day if I get bored enough, or if someone opens a PR to do this.
Could you please add a license to the repo? I'd like to use this in another open source project and well, I know I can use it but I'd like to have the official confirmation in place.