I agree on adjusting the gain, that doesn't seem like the resolution to my issue.
I am going to research more with my staff and find out if there are quality issues intermittently on normal calls, and if so, that makes me think about a bad PRI channel. I don't have a spare PRI card, but I could maybe get one from eBay depending on the cost. We are actually switching PRI providers in about 120 days for pricing reasons, so that could "fix" our issue as well, if it is in fact with the PRI.
As for analog lines, I don't have a quick easy way to do that, unless I want to have lines installed, because we don't have any currently.