Is it the 6A fuse or the 2 A fuse?
1. look carefully to make sure they haven't been swapped and you have the 2A in the 6 a hole.
2. I assume you have replaced the tubes or swapped with your other monoblock to see if the problem follows the tubes.
3. I can't tell from looking but make sure you have slo blo fuses (unless Pathos specifies fast blow, which wouldbe unusual.)
4. If indeed you have the right fuse and it keeps blowing during service then you have a proboem. Vendors generally size uses with plenty of margin not to blow. You could call pathos (yes, it is a pain to get ahold of a real person at any company) and ask them. They might have decided it was too small and recommended the next size up. But not likely.
Where are you located? In LA, I'm pretty sure upscale carries pathos.
Good luck,
Jerry