Also a no here for the Spinfits.
Either go with the stock tips, then either Ortofon or JVC Spiral tips - imho.
CA Ken recommends silicone tips with the Nova. And as Currawong noted: get tips with wide bores.
True. But for multi driver IEMs they need the lowest possible output impedance or they go bananas.
Look at the classic graphs of the triple fi 10s at different impedances.
Single drivers aren't such a problem.
Lower output impedance (one or under) closer sound to what the maker intended - esp with IEMs,
2-10..... Output impedance usually some bass roll off or flabbiness, perhaps some detail loss.
Sometimes very noticeable other times not so much.
My Centrance Hifi-M8 has an impedance switch for 11, 2, 1 output impedance. Its fun to play around with and note what happens.