Serious SFM issues with large volume

So I have a pretty large AFP shared volume on one of my windows 2003 servers. The volume is about 910GB and contains about 800,000 files in around 1500 folders. Right now I'm using Microsofts SFM to serve these files to the macs on our nerwork. Since there is imbedded data in these files, AND since the clients are running a classic mode application that must access these files unfortunately SMB is out of the question. However now no users are able to see new files or folders placed within the file structure. From what I have come across so far in my search the answer is pretty much "SFM is a disaster, don't use it". Well that's understandable from what I understand SFM uses an OLD version of the AFP protocal. So I started looking for some alternative solutions and found ExtemeZ IP and MacServerIP however both of these products are fairly costly. Are there any other alternatives that I should know about? Any help would be most appreciated.