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Well I have owned S1 B&WDM601s and they are pretty versatile speakers, I remember trying a few amps through them and they all fitted pretty well. A deciding factor in choosing your amp will be what music you listen to. Arcam used to be the first choice of amps to pair with B&W speakers. Im not the best at suggesting systems due to the haphazard way of building systems I have. Maybe someone else could give you more support.
I have owned Pioneer, Arcam, Rotel and Marantz so I know how they sound with the DM601s.
Arcam Alpha 8 or 9 are good choices and shouldnt cost you more than around £150. They would be my 1st choice with your speakers. The Alpha 7 to 9 were the peak of that series, with the 9 and 10 deviating slightly from the warm sound of early models.
Marantz I have experience of, but only their CD players. The are traditionally smooth and slighly warm sounding. But not as much as that era of Arcam.
Pioneer - I have a SA-500a which cost me £30 but is such a wonderful amp. Warm and tubey sounding. Sparkly highs and a lovely full mid-bass. I dont know how the 608 will compare however as it came five years after the 500a model.
Rotel are good amps, but imho arent warm sounding.