I've got a question....How different does an 80's Dyna sound from a passive Foundation?
In passive mode they sound basically the same. Same PUs with VVT on the Foundation and VBT on the Dyna. There are some very minor differences in tonality that can be had with VVT that can't be had with VBT and vice versa. As far as the preamp, it's one of my favorites. Extremely versatile, IMO. I have 11 Peavey USA basses with that pre (or the RJ IV variation) with Super Ferrites, passive P/J, active humbuckers, passive VFLs or active VFLS and like them all.
If you can buy a Dyna at about the same price as a Foundation, get the Dyna. Battery life is only about 80 hours but it is 1980s tech.