I agree that some ARC gear sounds better than other ARC gear. I have used their preamps since the 1980s and their DACs. I found much better DACs. I think their preamps are some of the best around. I like the sound of the DAugostino preamp (the really expensive one) better but not enough for the cost difference. I have found ARC preamps to be very reliable. Since the 1980s I have had to send just one preamp in for repair. It turned out to be a broken wire in the umbilical of my SP-15 preamp. I used a SP-6b for 14 years and the SP-15 for 18 years. I had a SP-9 for a year or two. It didn't do much for me. Currently using the Ref 5SE. Yes, the 6550C runs very hot and that worries me. I have good clearance over the top of the preamp to allow plenty of airflow. I don't run that tube more than 2000 hours.
I hope that ARC is able to recover. It all depends on how much the new owner is willing to invest and how long the new owner is willing to wait for a return on that investment. I watched MF's video tour of the factory made last week. Looks like they have lost some engineering/technical talent. I also noticed they are struggling to release their new high powered Ref tube amp that was slated to come out about a year ago. The company will be treading water for a while mostly building current product and service support. Supply chain is a huge challenge these days and consumes engineering support to work with suppliers and replace discontinued items needed for production. Provided the new owner invests and ramps up hiring it will still be several years before they are able to release new products. Will the market be patient enough to wait?