You say the latest firmware, but is it actually? The latest release is 061.121.225.06100 which is 4 full releases newer than the General release posted on Xerox.com.
That release is here , just use WC75xxSpar for the release code.
If that fails, or is what you are currently running anywhere, your best bet is to share the same folder via FTP and have the printer access it that way. This way nothing changes on the client PC side.
What you are seeing is not a normal condition, but it would be very hard to get to the bottom of this as it would make for a very large Wireshark trace.
I've seen other posts on this forum about similar issues but I can't seem to resolve this one.
We have Windows Server 2012 setup as a file server and we have a 7556 that can scan to it. Everything works well but somedays it takes 20~ hours for a scan to finally show up on the server. I've followed this troubleshooting script but it did not resolve. We are using the IPv4 address instead of hostname, ports are open, newest SPAR has been loaded. I've talked to Service a few times about this but we never really get a resolution. If I reset the Server and the Machine then it'll work fine for about a week and then poof, back to 20~ hour processing times for 40 page scans. Service did stop in and did an ALTBOOT firmware upgrade to make sure it wasn't a corrupted upgrade but the issue still persists.
I've done a bit of research on the issue and the only thing I really haven't tired is forcing SMB 1.0 vs the 2.0/3.0 stack.