"Variants of this question have been covered to death on this and every other color grading forum. The answer is always the same. The only way to get a [proper] image you can trust is to run SDI [or HDMI] out to an accurately calibrated reference monitor. Grading by viewing the image in the GUI just doesn't work." - Jamie LeJeune
What's your hardware ... and ... are you running a monitor set to video sRGB and calibrated with a puck/software system for Rec.709?
How are you determining you're losing quality? If you check the re-import into project box when exporting, does it show the same as the original?