If your router has a samba server installed, then it -the samba server- is supposed to serve as interface to windows machines. If you are using a Porteus machine to connect to your server, i don't see what is the samba server for.
Maybe you have a windows server and you have samba installed in your Porteus machine. This is the "reverse" case and I have tested it in my office, too. But that works only in text mode; you get a prompt like that:"<smb>... or similar.
Maybe you should explain exactly which operating systems are you using.
A. external storage mounted in router with DDWRT + Optware
B. stick Porteus v1.2 KDE
C. stick Porteus 2.1 RC1 KDE
to mount storage to be accessible, locally in /mnt/xyz Porteus OS
A+B+mount.cifs = OK
A+C+mount.cifs = NOTOK
So, I consider Porteus team have great job with new KDE and I do not want to keep you busy with my dreams...
If I will find why is not working, I will post. Maybe a reinstall of RC1 KDE is the sollution. I suppose that the router is OK, because it's working with C.
PS: Sorry I complicated things, maybe I shall edit/delete some of my posts
Porteus-v5.0. rc1 MATE. Thank you all dev team and @Blaze for helping to configure it, thanks to entire Porteus community members for great topics.