I use a transformer based passive pre, a clone of the Music First audio baby reference, with an Audio Research ref 75 power amp and I have to say, I am more than happy with it. I compared it with an ARC Ref 3 pre and they were different rather than 1 better than the other. The Passive having a more detailed, refined, neutral sound, the ARC a bit more slam and dynamics. I don't think you can easily get away from the accusation that Passive Pre's lack some slam, but you make up in other areas, including price.
I have read lot's of arguments for and against, transformer based and resistor ladder approaches. The latter is the cheaper option I believe. Top quality transformers from Stephens and Billington, are'nt cheap