I own the following ARC gear: LS27, PH7, PH8, SP20, SP10, SP15a, LS8Mk2, VT60, D60, 2 D240Mk2, D400Mk2, Ref110, Ref150, CD3Mk2. I listen to the stuff in various configurations with the only limitations being the Ref110 and Ref150 do not have a SE input and the SP10 does not have balanced outputs. Everything is connected by either Litzlink and Litzline (both black and grey jackets). I use a HO version of a Dynavector xx2mk2.
Reliability: I never had a problem w/any of my equipment that is the backbones of four systems. One of the D240Mk2s has a solder joint issue that occasionally causes a 30 second or so disruption.
Sound: The newer stuff is quieter. The Ref150 is in a class by itself. The D400mk2 is the best solid state amp I have ever owned and it has much better bass control than the REF110. The LS27/PH8 combo is much better than the SP20. The SP15a is a very strong contender. The SP10 is not as extended in both ends and sounds artificially euphoric compared to the LS27/PH8 or the SP20.
I have not compared the PH7 v PH8 v Phono stage of SP20. I will also eventually get around to using the PH6 with the SP15a and SP10 linestages.
Thoughts??