Thanks for the tip Greg, I read it after I had already played for quite awhile, and I didn't notice sloppy timing, but I was pretty much just zoning out on what a cool instrument this is.
I checked out a number of things:
1) A/B-ed it to my Studiologic VMK188plus as far as keyboard action and responsiveness with Pianoteq. The Casio reaches higher velocities easier with Pianoteq, a little too easy for me right now, meaning some velocity curve adjusting in Pianoteq. Both keyboards feel quite good to me. Initial impression is that I like the Fatar a bit more, it seems deeper, and I can dig in a bit more. This may entirely change with a new velocity curve. If possible I'd like to replace the Fatar, because it's electronics are flaky.
2) The main two piano sounds are excellent. I've been using Yamaha's almost exclusively for live digital piano sounds: Motif's, P60, P85, and at one point an S90es. The overall brightness of the Privia sound is a welcome change, and I'm thinking it will sound outstanding live.
3) I tried Luc's suggestion of using a single amp along with the internal speakers- it sounds terrific! This is just using a small Peavey KB1 amp with 20 watts RMS and weighing about 17 pounds at a low volume so things blend, emphasizing the bass.
4) I hooked up Pianoteq to the internal speakers of the Privia, going midi out to my netbook via USB (tried standard midi to USB also) then using either netbook onboard sound or an E-mu 0204 external soundcard back into the Privia. They both sounded quite good through the Privia internal speakers, however Pianoteq didn't have as much bottom end as the internal sounds of the Privia. There was also low level ground noise from the speakers until I hooked up a hum eliminator in series, then sound was super clean. So, it's good to be aware that this type of hookup creates a ground loop (at least it did for me, whether using an AC adapter on the computer or not).
These are just first impressions, but I'm already loving this keyboard!