I don't have any equipment that I could hook the W100s up to unamped.
And I'm using an ETA42, the predecessor to the META42... (runs off 2 9Vs, 470uF rail capacitance, BUF634 railsplitter buffer, non-stacked EL2001s, 1uF bypass Wimas, no multiloop or class-A, Dale Vishays everywhere, Panasonic EVJ volume control, Neutrik locking 1/4" jack, cheapo $2 RCA jacks, AD8610x2 on a Browndog, Wima MKP10 1uF input DC-blocking caps, Apheared resistor values)
The HD600s sound pretty dry and bright in comparison. Unfortunately, the *really* smooth and creamy (not much detail at all, maybe even some distortion)mid- to lower-mids isn's something I like. However, for vocals and Gershwin, you don't notice it very much. I haven't tried any jazz yet, but I'd imagine the W100s would sing.