I did some searching on the 'net and found that Synchromax seems fine for BMWs M5 Getrag transmissions (which also have notchy clashing shifts like our cars). Because it is an ATF weight lube, the added friction will enable the synchos to grab better, so smoother shifts with less clashing. My concern is that, unlike the M5 Getrags, our transmissions share lube with a limited slip differential. That part of the box is going to need gear-lube with a "GL" rating and friction modifiers for the limited slip. Here's where our problem seems to lie.... the added viscosity, lubricity and limited slip friction modifiers are NOT conducive to smooth synchronizer functioning. The stuff is too slippery and thick, especially cold, especially in 1st and 2nd which are triple synchronized (I think).
I want my gearbox to shift "smooth as butta" too. It should. A car like this requires a smooth shift to fulfill its potential. However, I don't want to go wiping out the differential to accomplish this.
With the conflicting lubrication requirements within our transaxles, a proper compromise is essential. Maybe one of the Royal Purple products is it. Maybe it's Synchromax. Maybe it's Gear-Max.
Anyway, I think this is a crucial topic for our cars. Heck, maybe this is the reason Maserati chucked the transaxle in favor of an automatic.
My only experience so far is that changing whatever the PO had in there to Mobil1 75W90 yielded a very small improvement in the inadequate notchy clashing 1-2 shift.