It's 100% new. The old content is shunted to the side as Miroslav 1, and isn't even the entire instrument as it's missing the all-important breath control patches that made that library so unique. So I advise keeping your Miroslav 1 or Miroslav CE (including the versions imported to SampleTank's latest version).
It does, however, appear that Miroslav himself was involved with the new project (although they don't really get into that), as the string bass pizzicato set has one patch called "Bass Pizz Vitous Style" which is their cue that this is the jazz version of pizzicato bass.
I have just evaluated that specific patch (but no others) in the context of my jazz project, and can't use it for two reasons: the reverb appears to be baked-in (I can only find EQ settings to edit), and they didn't put a hip-shot on the bass so it only goes down to "E" (I need it to go down to "D" for several songs, and might eventually need it to go down to "C", which is pretty common for hip-shot extenders).
The timbre is quite nice, and that specific patch takes a bit over 70 MB in memory when loaded, if that says anything about the depth of sampling (in other words, not on the level of VSL, but not what you'd get on a Korg M1 either
).
I am able to tame the resonance and darkness of VSL's Upright Bass Jazz Library (separate from their orchestral bass pizzicato patches) pretty easily using Vienna Suite Pro plug-ins, so it's no big deal, and their bass does sound almost identical to my own upright bass, so it would even blend well if I did a mixture of live bass and MIDI bass.
The Vitous bass is quite warm but is miked properly and played well, unlike most so-called jazz upright bass libraries out there that seem to be recorded by people who have no exposure to the genre (especially in its breadth and history).
At any rate, the room ambience of the recordings was a criticism in that positive review; that there was more control of ambience in the original edition. Yet it isn't an echoic space overall; just not what I'd want for an intimate jazz recording. So it's really only a problem for the Vitous pizzicato bass.
Overall, this is a warm library, not at all bright, but without the vibrato that was common in the original edition. Possibly they felt the market was mostly western and not familiar with eastern european preferences for vibrato on orchestral horn and other instruments.
I also suspect -- based on some limited tracking with flute, bass, cello, and a few other instruments -- that it will make for a more realistic sounding "first mockup" sound source, and with way less trouble, then many other libraries.
So I tend to think the positive review that I found, has correctly identified this library's strengths and that it is worth the upgrade cost but maybe a hard sell for fresh buyers given the competition.