ORFS (OriginalSamplingFrequency is the tag) 44.1 would technically be correct… as the original file is a 44.1kHz MQA file.
Some companies use OFS (Original Frequency Spectrum) as an indicator confirming the stream is MQA as well.
It’s all part of the wonderful MQA mess of a format. 
Because that’s what the master file used to make it was and is how any MQA DAC shows the ORFs the rest is all upscaling trickery. As for what your DAC finally does with it is anyone’s guess as that stage is a black box, it might be 44.1 or 88.2 or 176.4 or 358.8 or ….