Got it... well, it's done. DL'd FV v46, uninstalled all previous drivers and inf's, and installed the new drivers via DevMgr and it's all go. Nice!
So far tested Hind and Apache Longbow [both 3dfx v2 patched] and they run nice and smooth though still exhibit the exit game bug where you need to close out with an Alt+Tab, then kill the process with a CAD. At first Apache didn't want to run with SLI enabled so I swapped the cards, putting the new 3dfx card first and the older Diamond in the 2 slot - that seems to do the trick.
Also tried EF2000, which *had* been running on the single V2 before [and without environmentals in Autoexec.bat at that], but it doesn't run now in any card position, with SLI enable or disabled. No great loss since the primary graphics card is an S220 Rendition Verite and it runs nicely on that chip, as does Indycar Racing 2 Rendition.
This retro box is geared more towards dos and early 3D games that have a tricky time with either W98 or the V5500 which forms the core of the main retro rig - that handles Grand Prix Legends, European Air War, Half Life etc... thanks for the pointers all..