I haven't heard Audio Mirror but I do have an Ayon, another 6c33c amp made in central Europe with polished stainless steel. My complaint about the Ayon is that it has too many features. I feel like the swiss army knife approach touches the signal too many times and detracts from soundstage and clarity. it does have fuses in the signal path to protect the transformers from a blown tube and I'm thinking I'll jumper those out and it should sound much better. Don't get me wrong, it is a great amp. But could be better.
I like the 6c33c tube if you have air conditioning. 2 x 6c33c per channel will be about 400 watts of heat into the room. the LM runs hot too. so make sure you can handle the heat before buying either of these. I don't have air conditioning.
I'd love to hear them and think you should listen before you buy them.
Jerry