I have owned ARC gear for over 30 years and have not had any reliability issues. Some years ago I had a 6550 go that took out a resistor, but that is about it. I have had absolutely no problems with my Ref 5se going through tubes. My Ref 2se either. The Ref 10 was probably just a fluke. Maybe a poor batch of tubes or something. Was the Ref 10 sent in for service to the ARC factory? They are usually very thorough.
I have had other gear in my system from time to time but always went back to ARC. There is just nothing that compares to the sound of their preamps. I would go for the Ref 6se if you can. Long term I doubt you will be satisfied with something else.