Did you mean MacIntosh mono blocks?
I have both Audio Research Reference 160m monoblocks and the Reference 160s stereo version There is a small but notable difference in sound quality.. a bit deeper soundstage with smaller and more spaced apart images, surprisingly the stereo version sounds more powerful. You can see my system under my UserID.
If the question is if you can make a big difference in switching to a different brand and monoblocks. Then, you can make a huge difference… depending on your taste in sound. I am familiar with an earlier version of the Maggie’s. Also I was listening to an MC462 this weekend.
For my tastes very large differences can be gained, for me it would be positive. More detail and better tonal balance (more detail and more balanced treble) which should make them image better, if that is what you want. But those would be brand changes… if it is simply the mono versions of the same amp, I suspect your experience would be similar to mine… small, but notable. But the actual cost may be very high if your decision is not choosing between one or the other at initial purchase.