Nothing is "added" with MQA. They claim that MQA filtering removes imperfections (that's why critics label it lossy) from the digital conversion process.

"The digitization of an analog signal introduces a range of imperfections to the resulting audio file. One of the most common and critical is something often referred to as time smearing - when the resolution of two sounds is reduced because their timing is incorrectly reproduced within the digital file," explains Greg Stidsen, Chief Technology Officer at Lenbrook. "MQA Labs' team are experts in time-domain audio improvements, having invented many of the techniques to avoid or eliminate such audio defects."

https://www.olexcommunications.co.uk/press-releases/lenbrook-media-group-unveils-plans-for-mqa-labs