I have tried the Spectron Musician III MK2 mono-blocks with a TVC unit and the Benchmark DAC1 Pre. None of these have the finesse that the Joule Electra 300 ME has, but the sound was still great. I never got a lean sound with any of these preamps. In my experience and in my system, the sound can get lean if I use higher gauge (12awg or higher) speaker cables. This is due to the Maggies demanding lots of current, which the thinner wires simply can't deliver.
I have not heard the Pass Labs XP20, but I doubt that the sound will be anything less than stellar with the Spectron amps.