System advice

ISSUE: Change your MONITOR speakers or change your NAIM electronics 

Somebody gave you some dodgy and incomplete advice by ignoring key influencing factors and pushed their fave NAIM bias on you.:

All brand components have their own bespoke sonic signature , That’s why system synergy ( or conversely a lack of it …) is so important when cobbling together a full system. 

NAIM electronics is a fine brand that is one that polarizes listeners. When you do your research , you may find that NAIM’s sound divides the listeners into either a love it or hate it camp. One size does not fit all ….Sure ….NAIM can sound lovely with certain speakers, but yours don’t seem to fit.

My personal audition experience with MONITOR speakers and also my observations with them at audiofests suggests MONITOR is a better suited to avoid  NAIM ( see polarization divide above) . CYRUS and MONITOR were paired at an audiofest I attended a couple of years ago.

Others I would audition are 

• Sim Audio Moon 
• Musical Fidelity 
• Cambridge Audio
• Exposure
• Arcam ( you already know how much you liked this ,,,) 

Alternatively…. Yes …. NAIM can be a fine partner with numerous other Brit speaker brands . Think HARBETH, SPENDOR, ATC ….

TAKEAWAY

Go audition alternate stablemates to MONITOR , or conversely audition better pairings  with NAIM . There is no singular silver bullet magic solution in these forums. 

Some drive Fords….some drive Chevys. 

I am sorry to hear that your upgrade did not go as planned. I am not familiar with the sound of Naim equipment, but regardless it is on the low end power-wise for the speakers. I could not find exact specs on the speakers as there are a lot of Monitor Platinum models, but I am guessing that the impedance curve is probably not favorable for the Naim amp. Based on what you feel is missing from the sound, I suggest starting with a new power amplifier that has more wattage, and performs better at lower impedances and is known to have a touch of warmth. Budget will drive your choices of course, I highly recommend looking at the used market here and on USAM.  

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).