QoS settings to improve quality?

Currently in eval period with VOIPo. So far everything is working pretty well. On one long call, did have a period of breakup/stutter, but not severe. I'm wondering if some QoS changes could improve situation. I have a Linksys RVL200 router, Have VoiPo provided Grandstream HT502, currently behind the router, setup in the DMZ. I'm not familiar with QoS settings, but looks to be an ability to dedicate bandwidth, and apply some level of prioritization to the ports. A lot of settings beyond that I need to get a handle on. I do have a number of other PCs and Netflix on-demand that could be downloading a good amount of data, and PCs uploading data for online backups.

Currently on Comcast Cable Internet connection, so of course much of the internet latency/bandwidth is out of my hands, but want to control what I can on my side of the network.

Anyone have any thoughts? Tried searching for QoS topics in the forum, but didn't find anything.