Your B&W speakers need quite a bit of juice, no smaller foot print amps can do the job nicely, not at the same price level anyway. At much higher price point, there may be integrated amps that can handle lower impedance loads on similar or smaller foot prints. Another thing is, you obvious believe in Marantz has a certain sound (a myth from the good old days, but quite understandable
..) so your choices are more or less limited to what you can find on their website.