The capabilities of the Meridian gear is complicated and not always identifiable, so the Roon default is No MQA. You may have to set it right. Sounds as if you have it right, Roon passes the bit-correct bit stream to the Explorer which unfolds it and renders it.
Meridian gear doesn’t do rendering of MQA that has been unfolded in Roon. In this case, because Volume Leveling changes the bitstream and therefore breaks MQA hardware processing, Roon automatically takes over the unfolding to 96k, but in this case the Explorer can’t render it higher. Allegedly Meridian is working on adding the rendering mode.