It depends on what you think is missing from your large set up? 7200s would seem to be an easy replacement for your 5500 and no need to change anything else. It appears that Meridian are focussed on in walls for the time being so I would guess no replacement for the DSP7200 expected, making them a better long term purchase. But I would go back to my first question, consider perhaps a sub? or just buy the 7200s and enjoy without expecting too much change.(Then you might be pleasantly suprised)
Happy listening