It's the old "tubes vs solid state" debate. Take your pick.
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The Rogue 66 is a romantic unit, with fairly good detail but a plump mid-bass but lacking solid low bass. I've used both in a couple of different systems and prefer the Adcom unit for its accuracy and greater power at the frequency extremes. That said, the Adcom is not a lush sounding piece and can sound a bit dry in some systems.
Personally I prefer (and use) the discontinued Parasound P/LD-2000, a class-A, solid-state preamp designed by John Curl. It provides great dynamics, power at the frequency extremes, and is somewhat harmonically sweeter than the Adcom, especially after it's been on for a few days. Sometimes these pop up on the used market for around $500, which is a great bargain IMHO.