Pass designed Preamps compared to Tube Preamps

Has anyone compared any of the pass designed preamps, specifically the Aleph P, or some of the older Threshold, Fet 2 sii, 9 and 10, to tube preamps. According to a lot of reviews and write-ups, the Pass preamps possess a warmth that rivals tube preamps while still offering excellent clarity and detail. Can anyone offer any head to head comparisons or experiences?