I have the HR 824 Mk1's. I also use Amphion One15, which are a noticeable step up from the Mackies.
Have you considered other monitors from ATC, PSI, or Amphion (passive). All of them are in the same league but with different flavours. Amphion sells matching amp and cables, so it's like getting an active, but out of the box.
Gearslutz has a lot of feedback on the 8351 and comparisons against these monitors. You probably want to read them all as the results can vary, but I think you'll find the general trend at the end.
From what I hear, the 8351 is a step up from their traditional 80X0 series. After my research, for me it had come down to ATC SCM20 ASL Pro Mk2 and Amphion.
How big is your room? Are you planning to just listen or do work on these? What does your listening triangle look like?