The ECL86 stocks are dwindling but they still can be found. Sennheiser have dropped them as replacements for the HEV90 for the PCL86 which require rewiring of the amp boards. "Something" happened in 2005 which made them react like that...
The HE90 doesn't really care for amps that are too honest. It is a highly flawed transducer engineered for a certain sound so I'd use the Aristaeus with it.