From your PC to NAS you get 22MB/s but from your PC (or NAS) to the EVA9150 you get 4MB/s? I would first check to see what type of performance other people get r/w to the EVA9150. Maybe its just slow?? If thats not the case, try to confirm by hard wiring the EVA as a test to see if performance improves. If it does, then you need to start looking for issues in the wireless N setup or maybe the distance is too far.
Maybe the EVA has a firmware upgrade?
Yes i get only 4MB/s using wireless N to the eva 9150,i havent try'd wired,the eva has a 100mbit nic.
I'm using the latest fw on the eva,with that i can use nfs wich has a slightly better performance then samba,other people report arround 70 Mbp/s but that's wired,wich i rather not use,the 825 and the eva are in the same room,so distance is about 4 meters max.Altough the speed seems slow,i have no problem streaming m2ts files with max bitrate of 40mbit.