From the sounds of it, your low OG is probably not entirely caused by your pH levels although if it is truly at 6-7 after mashing you are going to have issues with conversion, and ultimately the amount of fermentable sugars available in the wort - From what I understand the starches would still affect your gravity readings, which still makes me think that there may be other forces at play...Your low sugar extraction could be one of many things...How do you rinse your grain? What temperatures do you use?
As a quick and easy way of getting the desired pH level (optimally 5.2), you can adjust with food grade phosphoric acid...others might recommend a product called 5.2 stabilizer, but I havent had much luck with it - I typically use RO water with the addition of about 1 tsp of calcium chloride and always hit the proper pH without adjustment
If you want to see if you are actually achieving a good conversion after mashing...try an iodine test - Just remove a small sample and place a couple drops in the wort...If it turns black/purple it means that you still have starches present, and would most likely need to look into adjusting the pH...otherwise the iodine will just dilute
Hopefully this is helpful...otherwise I apologize for the rant