It seems to me that geometric fonts pair well with most serif fonts and some humanist sans-serifs since they are of considerable contrast, but I don't have a lot of experience with them.
Does anyone have any other suggestions or further insight?
I'm still learning and practicing with font combinations myself, but I go to inspiration sites for reference like typ.io.
The most common serif typefaces people chose to use with geometric fonts seemed to be rounder and have larger x-height, much like many geometric typefaces. Georgia was one example.
It would also probably depend on whether the geometric font is in all-caps or not, but it seems that in general, fonts with large x-heights would pair well.
The most practical way to approach this is to apply the following rules:
1) Less is more. If you can get away with one typeface and add contrast, that's even better.
2) Trial and Error. Somethings look nice on illustrator, but not as good on a website or on paper, so it's difficult to have a general rule for pairing and laying out typefaces. The best way is to try it and compare it with other tries.
3) Show and tell. The context and the density of the content, will affect it's presentation, no matter how beautiful the typeface is. So the best way to discuss this is to show an example that we can tackle together.
since they are of considerable contrast
That's pretty much it. It's not a science. It's "what looks good to the trained eye" is all.
Typefaces that are very similar often work together, as do typefaces that contrast well. It's that middle area in between where they don't always succeed as well. So, a slab serif and a serif might different enough to look odd, but not different enough to contrast well with each other.
One easy way to pick contrast is to have one face be a humanist or geometric sans. These are simply typefaces that are bare-boned and aren't out to win a fashion award. This gives you leeway with other typeface to be quite flamboyant.
It's a bit like fashion. A patterned tie looks best against a bare-boned plain shirt. Does that mean you can never mix plaids and stripes together? No. It's usually just not the best default option.
But having two overly decorative fonts together is where you get the awkwardness. So, a Bodoni and a Blackface might both try and compete for the spotlight too much. But there's always exceptions...at the end of the day, it's a subjective call and heavily dependent on numerous factors as well as taste.