I'm having trouble understanding what you're trying to do and what problem you're having doing it.
Intranet (as in local network, not Internet) connections are not affected at all by portforwarding, and I wouldn't be surprised if they aren't affected by QOS either. If you're trying to access your NAS from outside your network (ie, accross the Internet) you'll probably have to manually forward its port (QOS probably won't make that much of a difference with it).