Hmm... Yes those pulse/saw combinations look quite interesting. I imagine they sound quite wild.
I don't know... I think there are enough voices really, especially with the DACs and adding more filters is going to be a problem in the implementation (and probably the amount of FPGA fabric required). Its just that the range of tones from each voice is limited.
Even the Roland Gaia only has the three tone generators. Its just that it can do more with each of them than the SID can. Perhaps you might want to look at it. Being able to couple the filters from each of the two SIDs might be better than adding new ones. Having a "peaking" type filter would be nice too instead of just the low, high and band passes.
I've already spoken with Paul about adding a proper mixer so that we can set individual levels and panning for the SIDs and DACs. Mostly in order to properly support C64 mode and the mono output on the Nexys4 but it could also do the coupling.
Umm... Natural saw is usually more like this, I believe: https://1drv.ms/i/s!AgcNCnteKUeegQ2AU7P7hR-xe9IR
Perhaps not so pronounced in the curves at the top and bottom. I generated it by combining a saw and sine.
But certainly, a few different saws (whatever is possible) would be very nice. The combinations/variations would save the voice count required to get certain sounds so you wouldn't need so many anymore.
I might have a play with my synth later and extract some pretty pictures and examples of saw waveforms it generates so we can compare.