I quite agree. Retuning isn't virtually impossible: it's impossible. One fundamental difference between a piano and a digital piano is that the piano tuner can't be called in to fix any out-of-tune notes in the latter. There is the additional issue that the out-of-tune samples are always exactly the same, making the fault doubly irritating.
It would seem that the piano tuner hadn't been called in often enough when the initial recordings were made. Vienna Imperial is expensive, undoubtedly reflecting the undeniably impressive technical achievement, but this issue really needs sorting out, perhaps by another recording session to recapture the duff samples. In a concert setting the current Vienna Imperial would be barely acceptable; for an instrument designed for recording it is simply unacceptable.

Hi Eric,
I've been using the VI live in a gigging environment with my Macbook Pro (early 2008, 2.5GHz, 4GB RAM), with excellent results.

I've had no issues using both using the onboard sound and also using my Moto 828mkII (firewire), in both cases streaming the samples off an external 2½-inch 7,200rpm SATA laptop drive mounted in a USB "ICY box" (bus powered). I was anticipating having to replace the drive with a firewire unit, but it works flawlessly.

Also, the convolution reverbs built in to VI are lovely, but really, really processor intensive. So if you put the slider down to -∞ (i.e. off) the processor usage drops right down. If I use VI in either standalone mode or via Mainstage, there's enough welly to drive the convolution reverb, but not so in Logic where I use Logic's Platinum (non-convolution) reverb to avoid glitches.

I've been easily able to get down to a 128 sample buffer -- as you say, anything more than this starts to interfere with playing.

Since the current Mac Minis are of a pretty much equivalent (or greater) specification to my setup, I wouldn't anticipate too many problems.

Hope this is of some help,
Edward.

I've just spent a week with the Vienna Imperial and I love it. However I have a slight concern. To my ears at least, some of the top notes (e.g. the C and Db three octaves above middle C), especially when played quietly, seem slightly out of tune. This is only audible when the sustain pedal is down and the resonance samples enabled. Although this adds to the organic quality of the piano (to refer to an earlier post) it does worry me, especially when this is to be used in recordings. Anyone else noticed this?