Can a plant live on Potash alone? There are several things that can cause a plant to drop its leaves and die. Starving it is one of them! At this time of year, it could also be winterburn.
New foundation? Sounds like they sold off your top soil and left you the subsoil junk. This is a little something that architects should specify in their drawings to protect the homeowner - Stockpile the topsoil on site. You will have to do something about that. PH6 is acid but within the range for acid loving plants.
Who tested your soil? How was it sampled? When was the shrub planted? Is anything next to it surviving? Are you sure N + P = 0?

I think this is an alkaline plant and we planted them in the fall of 2005 one died ,replaced it last fall and now they are all showing signs of stress. I tested the soil following the directions carefully.We amended the soil and planted them high. We watered them very carefully. I just can't figure out what is wrong, even the garden center is perplexed.

In any case, it is an adaptable plant and can live in a range of PH.
You say you amended the soil. So is N and P still 0? Did you test it again?
Can you post pictures?
My first guess is this is winter dieback. Did the damage occur during the last weeks of cold into the warming weather? Are they exposed to winter sun and wind? Are other nearby plants doing well? Of the plants that were there since 2005, were the leaves healthy, shiny and lush last summer? When you amended the soil, did you have to replant the existing cherry laurels? Was there any signs of stress, infestation, wilting, webbing, discolorations including any part of the leaves or stems / branches? Any stippling on the leaves? Does the soil drain well? Since this is a new foundation, did you check for hardpan beneath the plants? Was there any ice encasing them during winter (not snow).
Anything tunneling beneath the area? A large population of grubs?
Once the growing season starts, they may fill in and be fine. However, if not, you might also dig one up and check out the roots for discoloration - looking for root rot diseases such as phytophthera.
If the plants do well this summer, you might try protecting them next winter with something like a burlap screen or Xmas tree branches. Search around these forums and you will read several methods different gardeners use.