Damn, Tom. I've asked this same question and never gotten a reply, so I conclude no one who reads AudiogoN has made such a comparison. I'd also like to know if there is an appreciable difference between a XA9000ES and a DVP-NS9100ES, but apparently no one has made that comparison either. The local (Santa Barbara) Sony shop doesn't carry either, and the two high-end stores don't carry Sony.
I have a 9100ES and 9000ES, and thought to buy either a SCD-1 or XA9000ES when the HD-DVD wars settle and I no longer need DVD coverage. I've been warned away from the older SCD-1 by one expert, another says they're fine if you keep them serviced.
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