Grole, welcome to the forum.

What inputs are you using?

A 568.2mm or basic G68 can be had for relatively little these days.

The HD621 will not synthesise a centre channel when fed a stereo signal.

Sooloos, Roon, G series (with LPS upgrade), 800 series (with LPS upgrade), HD621, AC200, Prime and PS, DSPs old and new.

Purdeys, Moke, Leica, 'Blad. Only the best.