The J2 arrived today, and it will be staying. Prodigious controlled bass, with cleaner midrange compared with the M2. Sand amplification + tube preamps have always worked for my ears. It's not surprising that it worked it's way back into the lineup. I'm sure at some point I'll get bored and put the KT-6550 back on line and be amazed, but right now this is a great combo for me. I think the Zu Omens at 12 ohms respond well to the solid state approach to amplification. The tubes were good too, but the bass suffered at times on certain recordings. Not so with this combo.
Hopefully I'm done tinkering for the Winter. Did I just say that?