I have no idea why I gave you a link to the benq forum (brain malfunction). Maybe it would be beter if you looked in the nec forum!!!!! Thier should be lots of info on firmware and good media in the nec forum.
Here is a thread on media and thier are probably plenty more if you search.
Personally, I have an nec3500 so I cannot say what is best for the 3520, but the 3500 likes just about any good media I throw at it. Some good ones would be verbatium 8x+r (mcc003), verbatium 16x+r (mcc004), maxell 8x+r (maxell002), maxell 4x+r (ricohjpnr01), fuji 8x+r (made in japan only so check the label, yuden000t02).
By the way, I havent used any ritek 8x media but the ritek 4x I have burns very well. Your drive can do error scaning so why not do some scans and see exactlly how well the ritek you have is burning? If you are not farmiliar with scanning, look around for mention of cdspeed error testing in the nec forum. You may have to have a specific firmware for it to work.