I used to have B&W 705s with Meridian amps and processing. I would never go back to passive speakers, there are just too many compromises for me. The HD621 will give you access to HD audio codecs, albeit not Atmos but even vanilla DTS sounds epic on most movies through M DSP speakers.

Chris
Srces: Wiim Pro | OSMC Vero 4K+
Procs: HD621 > G61R > Minidsp DDRC-88D
Spkrs: 7200.2 + 5KC + 5Ks | iNuke6K > USC15 | iNuke3K > 2 x Crowson T108SS
Video: JVC HD950 & 1.9m React3 2.4:1 screen
Room: 5.8x2.8m | Various GIK Panels