Classe CA2300 is a good match, which I have used for few years with 803D/Diamond speakers. Smooth, detailed, neutral. Bass extension is very good, but not as good as e.g. Devialet.
Classe preamp+amp will exceed your budget unless you consider use a good cheap DAC with volume control - but test compatibility.
Another option is Devialet all in unit - superb sound for modern compact package.
Also I previously used Marantz successfully with 803D - consider the PM11S3 or PM14S1. Marantz reference test speaker is 800 Diamond, so their components are well matched and voiced to drive the B&W range.
Finally just want to highlight that the 803Diamond is a superb speaker that rewards every upgrade or tweak - well balanced, easy to listen, and reasonably transparent. Sound quality also improves with running in and will improve up to 6 months.
Classe preamp+amp will exceed your budget unless you consider use a good cheap DAC with volume control - but test compatibility.
Another option is Devialet all in unit - superb sound for modern compact package.
Also I previously used Marantz successfully with 803D - consider the PM11S3 or PM14S1. Marantz reference test speaker is 800 Diamond, so their components are well matched and voiced to drive the B&W range.
Finally just want to highlight that the 803Diamond is a superb speaker that rewards every upgrade or tweak - well balanced, easy to listen, and reasonably transparent. Sound quality also improves with running in and will improve up to 6 months.