That is almost certainly a burn in issue. To give you a little confidence that this is the case here is a thread from a few months ago. Note especially the change of the OP’s opinion over the course of the thread and the final two posts:
If the Bartok did sound lacking in transparency or “dull” as the OP originally found before burn in , then that would surely have been noted in the dozens of exceptional reviews that the Bartok has received.
According to this thread you have only had the Bartok for around 3 days. So you still have a way to go with even initial burn in.
This might just be me but I have found it worthwhile to turn off the item being burned in for a few minutes for a couple of times during the process in order to discharge the capacitors and to charge them again when switched back on. I suspect that the properties of the capacitors and changes to the dielectric are a big factor in burn in and this seems to speed things up a little. Please note that this is only a hunch and has no scientific proof. But it costs zero to try.