I have a similar situation. However, let me set the scene. I had no oil level issues prior to having the Lexus CSP piston ring service performed. The vehicle was under 100K miles at the time of service. Since that service was performed, I have also installed a K&N Typhoon Intake System and IL has raised the highway speed limit to 70 MPH. I am noticing approximately 1.6 Quarts of oil loss in between changes. I use Quaker State 5W-30 (non synthetic). The "low oil light" is being triggered typically with in the same week I change the oil.

I have concluded that there are too many variables to attribute it to one thing burning the oil alone such as: increased speed limits, more aggressive driving style due to sweet intake sound, lower-end oil, the use of non-synthetic oil on a high mileage vehicle (vehicle does not require it), no visual oil leak, new piston rings installed, the low level comes on right before the required oil change which does not concern me, the car holds a massive amount of oil for a 2.5 L engine (6.7quarts, I had a Grand AM 2.4 L and I think it held under 4 quarts).

I believe the manual says it takes 1.6 quarts to raise the low oil level and turn off the low oil level light. So, if you are only adding 1 quart it may come back on or stay on. Don't worry just add the correct amount of oil and then if it comes on again soon after I would get nervous.

 

Since your car burns so much oil, you should heck it more often. Back in the day people use to check their oil every time they filled the car up.
Btw the Porsche Cayman hold 10.7 quarts and it s 2.7 L engine, so 6.7 quarts is not that much.

 

My wife's 08 IS250 burns about 2 quarts in between oil changes (5000 miles).