Here's a follow-up:

Tried it out in the car, works great. Timing is odd on the intro to "Sledgehammer" though.

One idea that crossed my mind. Dunno if it'll work or not until you actually try it. But if there were a way to have it increase the volume logarithmically instead of linearly, it might sound more natural. For example, when there's a really quiet part, it steadily increases the volume at a fixed rate towards some specific target. If that increase were quick at the beginning, but slowed down its increase-rate as it got louder, it might not pump as badly but still deliver the desired result. Do you follow me? This might solve the "pumping" issue without needing too much read-ahead logic.

Another thing I noticed. Song fade-outs are interesting with this kernel because you get to hear most of the details of the fade-out at almost full volume. It's almost like the song doesn't fade out at all. There's the aforementioned problem where it simply "cuts" when it hits its noise-floor threshold, but once that's solved, fade-outs will sound cool. I like that because there are often interesting things to hear during long fade-outs if you listen closely.

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Tony Fabris