I am not the only person who likes Naim digital gear but not their amplifiers. I would focus on finding a substitute there. If you can get your hands on other interconnects and speaker cables you can try something different. Naim amps are somewhat sensitive to choice of cabling, particular the speaker wires. If that doesn't do it, look to what you changed which you did not like which is the amp and linestage. The components that affect the sound the most are the speakers, followed by the amplifier and then the linestage.
The only way you can determine what amps will do it for you is to audition some candidates, preferably by borrowing them and using them in your system. For solid state, I suggest looking at brands like Ayre and Lavardin. These deliver a sweet sound that is quite different from that of the Naim amps.
But, my own favorite amplification is tube amps, particularly lower powered tube amps. I don't know the specific requirements of your Monitor speaker, but, it is often the case that people are satisfied with amps of much lower output than they would normally consider when it comes to tube gear. I suggest that you look at an integrated amp from Synthesis Audio (Italian).