dBx has (had) a pretty bad reputation for "pumping" (or "breathing"), relative to Dolby.
I never cared for the sound of Dolby C cassette tapes, and I'd pretty much lost interest in cassette by the time HX-Pro came along (i.e., I really don't have much of an opinion one way or the other).
HX Pro certainly should help with HF extension at higher signal levels... which is the big bugbear when it comes to cassette tape in general and in any compander NR scheme (Dolby, dBx, what have you) in particular.
all the best,
mrh
