thanks a lot for your lenghty comment.
at a time I was in a quest for a global equalizer, and ended up installing an equalizer for pulseaudio. a little "cheating" to get a bit more bass and slightly less aggressive treble. it was not very easy to find and went unmaintained by its author, made the sound a bit "dirty" too. (similar to "issue with older versions of PA" you described).but even with PA - couldn't someone just write a compressor/limiter/leveling amplifier for PA? (in some mixer utility) this hardly sounds like a case, where we need a complete re-write of both kernel and user-space sound APIs to accomplish... if i remember correctly, isn't it also possible to do this with ALSA/dmix too?
your experience and advice about Jack is comforting. only I can't exactly find "Jack output" as an option in Firefox, VLC, etc. so this mean maintaining a PA/Jack/Alsa triad if you want to do everything.
maybe common software outputs to pulseaudio, whose output connects to jack (I'm looking at the description of pulseaudio-module-jack package in ubuntu/mint). then Jack layer is the "new pulseaudio" for programs that talk to it. then a global output goes to Alsa (or maybe to a network audio protocol, recording to file, output as a "web radio" etc.)
ideally, things should go wrong only if my Alsa driver is bad. ideally I could be using OSSv4 instead of Alsa and nothing changes (not only the OSS driver could be good, but OSS is available on other operating systems as well)
ah, I've noticed Jack is an option in Audacious, and in gnome-mplayer. not too bad
a strong issue is, it is hard to know what to blame when you fail at doing something or have a problem. is because of Alsa, PA? bug, configuration or bad quality driver? plus the common silly problems such as forgetting to select an input in a program or a volume set at zero.