If I remember a conversation with Alberto correctly the Tempo is simply a stereo version of the Audion, probably with a common but beefier power supply. I have two of them to use as mono blocks that also bi-amp.
If the Audion's and Tempo's are rolled off in the HF, I might now be able to hear it. I can't hear anything over 10k. But I think there was a model upgrade in the Audion at some point. Maybe wrong, but if so that might account for different perceptions.
I don't think Rick Shultz is modding GaN amps anymore. I had an LSA Voyager I was going to send to him, but he said he wasn't doing it any more. That was a year or two ago.
You might contact Alberto at AGD. He replies to emails to his site.