Hi Peterpan,
I can give you my opinion as i Have both owned the B&W 684 as the Monitor Audio rx/rs6.
I think the B&W is a great speaker with massive bass, but the Monitor Audio's bass is much more punchy and in control, the highs are perfect on the Monitor Audio, the B&W is a bit muffled.
I would advice NAD 355 with Monitor Audio and the Rotel 06se (or 1520) with the B&W 684.
I have changed my B&W too Monitor Audio cause I prefer metal music and the Monitor Audio is better then B&W. B&W is great with Dance music and R&B, Rap.
Other thing, the B&W is quite a large speaker so it needs room to breath! More then the Monitor Audio.