I bought 4 pair of spinfits off the reviews and wound up not using them on any iem I own. I never could get a really good seal with them. Since I have been on this kick with universal iem's I have learned a lot about tips and the fit as it can make or break the sound of any iem. I must have bought most of the tips available in the market and tried them all on several iem's I own. I discovered the fit is a very personal thing. What works with one iem for someone else may very well not be your best choice. Unfortunately, the only way to get to your personal best with each iem is to go through a lot of experimentation. On the 846 I wound up with the grey flex tips as my personal best and they sound great and fit me very comfortably. Might be a totally different experience for someone else.
I also changed the cable for a custom silver cable and got a noticeable improvement. I am not really a cable guy but this certainly made a positive difference with the 846. I have much more expensive iem's and I still feel the 8's are competitive and very enjoyable.
I still use the stock ones (the dark grey/blackish with that wax feeling). I think the Shure SE846 are super comfortable (once you adjusted the behind the ear cable correctly).
I changed my cable to the Brimar Quantum SXC (bought in Bangkok) and i also heard a noticeable difference. Though i think that the improvement that i heard for a 200 $ cable compared to stock might be a big difference, but i cant imagine that a 2000 $ cable would give me that much more (and i even take in account it all might be a placebo, which is also fine because i "only" spent 200 $ on the cable - it looks cooler and it sounds better - or tricks my brain - whatever).
Edit: Do you think it is worth going for a balanced silver cable and get a balanced amp like the RSA Protector ? Is the difference that huge compared to a standard silver cable upgrade?