From B&W 804 D3 to Focal Sopra 2?

I have a the Sopra 2 fed by a Hegel H390, 250 watts at 8 ohms.  PLENTY of power.  Room is 17X28.  Smooth, clear, extended and quite fast and detailed.  Chopin to Foo Fighters, Susan Tedeschi to Snarky Puppy .  Always dynamic and, most importantly, engaging.  However, there is also a pair of REL low frequency speakers.  (REL doesn't like to call them "Subs" because, as they correctly point out, sub-sonic speakers produce sound outside of the range of human hearing.  Hence the term "sub" as in "sub-sonic".)  My primary use of the RELs is not to fill in the very bottom 15hz in the music, which they do admirably, but is to relieve the main speakers of the responsibility to deliver fully their last 15hz, give or take.  All speakers roll off as they approach their bottom.  I have the RELs set to start engaging at around 50hz, I'm guesstimating.  A number of people here are suggesting low frequency support.  Don't brush it off.  Sorpra/REL combination is a good one.

@maxdukecapone I commented above that the size of the OP's room might be better suited to Sopra No3 over Sopra No2.  How do you find the native bass output from your No3's ?  What is your opinion on No2 v. No3 for the OP's room?

Anthem specs the amp at 550W at 2-ohm impedance so the STR will drive any speaker without any issues. When the impedance dips below 4-ohm you need lots of current and the STR provides that in spades.

My 803 D3 also sounded light. Nothing helped except adding two JL Audio subs. Much better. Even made the soundstage seem larger.

Erik mentioned off-axis oddities limiting the sweet spot. The measurements may suggest that, but in my room that is definitely not the case. Huge soundstage. Imaging is superb. The speakers disappear better and I'm hearing a larger, more stable sweet spot than any speakers I've owned.