Need help with firewall setting for SBG6580

I have an SBG6580 and if I set the firewall to Medium or High it blocks all ports except for commonly used or manually allowed ports but it also blocks a few things such as the steam login servers but not anything else related to steam, now if I set it to low it will allow basically everything so it might as well not even be there.

I've tried port forwarding, port triggers and even allowing everything using DMZ, so is it just impossible to allow services through this thing? Am I making a big deal out of this and setting the firewall to low is just fine?