One thing I forgot to mention was scale - the sound of the 5500's is much "bigger" than the 5000's - a large scale sound vs. a lot smaller with the 5000's.

Ever since I got the 5500's, I have been using some sort of DSP bass management. I used to use a very expensive Z-sys RDP-1
See my review with 5500's Rodneys Review and have continued using it till I got a Dspeaker antimode 2.

Right now I am fiddling with a Minidsp openDRC di which is $299 and does what the z-sys did and more, it works brilliantly with the Meridian system.

Apart from bass management, I also tend to find the Meridian speakers a little too polite and their inbuilt tone controls act too grossly, I like a very slight lift starting at 4-5k and up by 2dB at 20k. The treble controls on the speakers start acting much lower down.

Roon/Tidal, SBT, Trinnov ST2 , Twin Devialet D premiers, Vivid Audio Giya G1 Spirits, dedicated and treated room.
Meridian gear: 568.2mm and DSP5000's acting as TV speakers.