I finally found time tonight to thoroughly go through the new Shreddage 3 interface (and user manual) and to compare against the original edition of the Archtop Guitar, and after about two hours of that, I am definitely upgrading the rest of my collection, as this is too good of a bargain to pass up, given that it's really an entirely new product with almost ten times as many features as before.
As for getting the new version of Archtop closer to the old in terms of warm and bright timbre (necessary in many situations to avoid mud, retain articulateness, and to mix well with other instruments), that was what took me the longest, but I was finally able to abandon the old library and then to start treating Shreddage 3 as a new experience.
Although I had three basic starting points for the old version (50/50 bridge/neck blend, bridge-only, neck-only, and with or without amp as some genres work best with DI guitar even though I know many people think Nile Rodgers is the only one who gets away with that anymore), it seems the inherent levels are a bit different in this version, so for cases where I need a pickup blend, I am setting the neck pickup to -9.0 dB and the bridge pickup to -12.5 dB (overall levels are hotter now).
I didn't compare to see if different snapshots have different settings outside of the insert effect chain, but as I had little luck starting from scratch, I went through a few of them, found them all extremely muddy and boomy, but finally settled on the Archtop Bright Clean snapshot and heavily modified that to get to more of the Tal Farlow sound that is usually my basic starting point.
I'm not sure how much of this is pertinent to the other guitars, but hopefully it is helpful at least to those migrating to the new Archtop library. It looks like the feature set is probably pretty uniform between the different guitar models this time around, but I'll know more after doing the upgrades.
The main thing, for the Archtop at least, is that I find the Reverb, Chorus, and even Analog EQ, to reduce clarity. I tend to use my own plug-ins later in the mix chain anyway, so don't know if these are for convenience or are designed specifically to result in better mix-ready output that processing downstream of initial tracking. It's just my own tastes anyway, and also Archtops are quite different from solid bodies in almost all respects. I may end up finding I like the insert effects on the others.
I found that things were a bit more even and articulate in Mono, as I would expect for Archtop and even for most Solid Body work, but I'm too tired now to check other projects to see if I was ever using the original version in stereo or not. Usually I prefer guitar to be mono and center-channelled.
The tweaks I did to the Archtop Bright Clean snapshot before saving my own, were to turn on the Bridge pickup and use the balance described above, delete the Analog EQ, Chorus, and Reverb insert effects, switch the Twang to Mono Mode (and retain the Bright Mode switch), and use the Brit Combo U87 Mic in its On-Axis setting. I had previously used the Tweed Amp, now shown as S2 Tweed B. It's nice that at least the old amp models were retained as S2 (for "Shreddage 2") settings, if desired.
Having done this work, I feel very confident now that I know my way around Shreddage 3 and can quickly replace Shreddage 2 in unfinished projects with better results than before, even before I start making new works that take full advantage of the new features and use the new sound palette that is only available with the MUCH wider and deeper range of possibilities now on offer.
This incredible update/upgrade from Impact Soundworks puts their guitars (and probably basses as well), on top of the pile once again. The competition is fierce between the Big Three (Ample Sounds and Orange Tree Samples; others have good samples and some other features but are nowhere near as advanced overall, in my opinion), but I personally feel ISW is now the undisputed king.