The Coda is an awesome sounding amplifier but may be a bit too brightly voiced for the modern B&W diamonds which pair perfectly with the Mac amps. Mac and Diamonds are a certified dynamite match.
If your vintage of the speakers are not as bright as the modern versions then you might be better off to go with the Coda.
PS is your pre’s output impedance really 47K ohms? That means that the power amp needs 470Kohms to sound balanced following the 10 to 1 rule, something may be off here with their spec because neither the Mac nor Coda would be good matches electrically.
I would get that sorted and understood before buying any new amp.

