B&O produced a number of excellent decks - the Beocord 9000 is held up as the pinnacle but the 8004 and 5000 are also superb.
HX-Pro is a B&O designed circuit licensed to Dolby that extends the headroom extension of cassette tapes - this means that ordinary ferric tapes can basically accept more signal and improves the performance. The big advantage of this is that the tapes do not require decoding and can be played on any machine. It is not a noise reducing circuit.
DBX is a noise reduction circuit - a bit like Dolby B and C but which works on the entire frequency range. It can be very good but poorly executed versions can produce very bad pumping artefacts.