Yep, 6 PSI is far too low. Unless you're serving below freezing, I guess.
If you can't get good pours when the beer is
in the 10-15 PSI range, then your line lengths are all wrong. Too foamy means too short of lines. No head and too slow means too long of lines.
First determine how many volumes of CO2 your style of beer needs. You didn't say what style it is, so here's a chart. http://www.tastybrew.com/calculators/priming.html
Then look for that number of volumes at your known serving temperature on this page. http://www.kegerators.com/carbonation-table.php
For example, I'll if you were force carbing an American Pale (2.26-2.78 vol), you might go middle of the road at 2.5 vol. If your serving temperature is 41F, then your beer needs to be at just shy of 12.8 PSI or so.
Why did you force carb for 2 days at 30 PSI? Unless you have a Wheat or other highly carbed beer, you're almost certainly overcarbed at this point. Next time, try force carbing at 3x the serving pressure for 24 hours. In the case of this American Pale at 41F, you'd carb at 38 or 39 PSI for 24 hours.
For now, figure out the appropriate serving pressure and reduce your regulator to that pressure. Every few hours, burp the keg using the pressure relief valve until you hear the regulator groan. You can speed it up by shaking between burps if you really must. It's going to take a little time to get it back out of the overcarbed range, unless you were carbing exceptionally warm.