I've tried to use the dynamic expander in my Behringer, but have only met with very marginal success at best. Although it is in the digital domain and essentially a full-range expander (unlike the DBX which I owned back in the day and which has to split the frequency band up into the 3 hi,lo and mid adjustment bands), the problem I had with it (and with all such expanders) is that they only work not by increasing the level of the peaks, but instead by lowering the quiet parts of the music. So OK, you just turn up the volume once that adjustment has been made and you're in, right?? Well, not exactly...or even though that seems like a good idea on paper, in practice it turns out to be rather problematic and possibly for a number of reasons...but, the main one being that when you artificially reduce the quieter portions of the music (and it's the music I'm talking about here, not the signal, per se, but the sound) the experience can rather quickly become one of the sensation of 'throwing a portion of the sound away'...that is, if it is done at all too much, little or no amount of increasing the volume afterward seems to enable the effective recovery of those quieter parts to the whole picture...what I mean is, even beyond properly dialing in all the proper parameters, there's still only just so much impact a dynamic expander can have on CD or better, or vinyl, or even analog tape (although the latter seems to benefit the most...but then, even there, we're talking mainly about reducing tape hiss to just below audibility). I think it may not be appreciated in general (except by their owners) just how narrow the range of benefit to dynamic range such expanders actually are. To those outside of ownership looking in, it may seem as though there is a rational enough promise to them and that one could reasonably expect to begin to solve whatever sonic problems with them. But, the advantage I think is relatively small, in fact, all but inaudible, even regardless of their cost altogether, actually. I agree with what I think Almarg is likely referring to: that some recordings suffering from narrower dynamics to begin with may benefit a little more so and that most, if not all, of what we would consider as more nominally good or excellent recordings end up benefiting something less. And yes, in effect, there may be different ideal settings for different recordings.
FWIW, when I started building my current system almost 25 years ago (my, how time flies when you're broke...), I considered dynamics near the top of the list...still do. But, I ended up finding much more success with all the other factors influencing dynamic range in system building in everything from amp choices, to cabling, to power conditioning (big gains there) and down even to things like removing the brass binding posts on my speakers and hardwiring to the crossover boards. Taken altogether, I've since seen far and away much bigger strides in dynamics than I ever could have hoped for with an expander of any kind I'm aware of alone, all of which has been very satisfactory. Unless there's some magic bullet out there I've never heard of, I would think you could generally afford to let go of the idea of dynamic expanders when it comes to your overall pursuit of dynamic range. Other options may hold better rewards, IMHO. Regards. John