My personal preference, for whatever it is or is not worth, would not be for another library. I find PocketFrog to be fantastic and I'd prefer to see people continue to develop it. Myself and others have released some other primitive functions lately, you of course do great with Plus... if it could all be combined properly that would be great.
My only fear is that if anyone other than Thierry does it, then when he releases a new version, we'll have to go through the trouble of incorporating all the extension stuff with the new version.
Two solutions come to mind...
One is to ask Thierry to add all this stuff. I know he's busy with other things, and I'm not sure PF is at the top of his list any more anyway, so I'm not sure aboout this.
The other option is to add extensions in such a way that they can EASILY be moved into a newer version. Now, in the case of my extensions that would be very easy, just add the header to PF and an include and we're done. That's because my stuff doesn't actually modify any PF classes right now, although they should, just to add methods to existing classes, but again, a simple header file takes care of that. In the case of your sound extensions though, your modifying existing classes, right? Not just adding to them? That's where I think the problem arises.
Just like they say in business: God forbid you get hit by a bus... I mean, if a new version of PF comes out and your... not around...

... then I wouldn't be able to use the newer PF version and still have your sound stuff in it unless I went through the trouble of figuring out how you added it to PF.
In other words, and I should have just said this BEFORE I started babbling... I think we all need to make sure our extensions are very loosely coupled to PF wherever possible so that new version of PF can be sloted in with the extensions without any trouble. I don't think that's the case today.
...and so I said to Mr. Gates: "$640 billion should be enough for anyone!"