I did talk talk to zero audio and they have been communicating with me back and forth, but they asked me not to share our conversation. I'm going to summarize the points though. I think it's unreasonable of them to expect me to not share the main points we discussed. Not that it is much help. Here we go:
- They can't really say anything for sure without having their engineer inspect two different pairs.
- They can't inspect the pairs, because we are from the U.S. and warranty coverage is like zero audio minus the audio. ;)
- They've never heard of such am "unbelievably high" quality/failure rate in Japan.
- 6db bas variance doesn't meet their "very strict" standard.
- More specifically, they can't disclose the standards, but 6db is irregular.
- In Japan they are famous for the low failure rate.
- Variance could be due to damaged drives in long-transit.
- Variance could be due to dirt on the "damper cloth" at the end of the nozzle.
- Damper can sometime be cleaned with a "soft-cotton tipped stick."
- It is very possible there are fake tenores from certain sellers.
Also, they did say in the last message that there is a "characteristic variation as a manufactured product", but it is set low as to meet the quality they set for the tenore.
I might have been able to get more information from them if I was in Japan. There is a slight language barrier and the warranty coverage issue. If you bought them from an official Japanese distributor and have a bad pair or two varied pairs, it sounds like (from my communication with them) they are willing to have an engineer look into the difference and cause. But from the US we don't really have any options.