Sonus Faber monitors vs. ???

It appears that you have a very good, well balanced system. The Sonus Faber Domus speakers are qute good and probably well matched with the Musical Fidelity 308cr amp.

Unfortunately, and as I am sure you are well aware, if you do go to a more refined "better" speaker, you may well have to consider a "better" amp (and other components in your system) as well. The A308cr is gettiing a "little long in the tooth" and there are amps capable of better performance at quite reasonable prices in today's market.

I guess what I am saying is that at some point we as audiophiles should decide that what we have is "good enough"

Now, if you are like me, you will continually find need to try something different, (for right or wrong reasons). I have tried dozens of speakers (currently Avalon Eidolon and Sonus Faber Guarneri Mementos), but at each point during my quest, I have had to evaluate the speaker in relation to the other components in my systems and have found need to upgrade them as well.

ADVICE: borrow, beg, or steal some of the speakers you listed and perhaps others and see if they sound more to your liking in YOUR system and go from there.

fwiw, i've also been looking to upgrade my monitors and have recently auditioned the concertinos as well as proac tablettes, jmlab profile, paradigm s1, rega rs1, various dynaudio, quad 11L/12L. to my ears, the concertinos, while by no means a bad speaker, were less appealing than all but the entry-level dynaudios--somewhat slow and boxy, without the precise imaging of some of the others. the concertinos are also an older design; i imagine speaker technolgy evolves quickly. the real surprise was the regas, which are also the cheapest--despite a disconcertingly lightweight cabinet and generic-looking drivers, they sound really good--detailed, big soundstage and nice integration of highs and lows. i'm still gonna try some others (psb, usher, etc.), but i was impressed.
of course, just my opinion on a rainy saturday--trust your own ears.