You’re not really missing anything, roll expressions can only output a single numerical value for now.

But there is a bit of a hack you can do to simplify your rolls still. With an expression like “10d6!{6=[spite]}“  you get the number value of the d6 pool, and for each 6 it will roll a new die which only ever has a string value of “spite”. Because string values are counted separately, this is a way to count a pool and the number of a specific face from that pool.

As a fun bonus, you could make your own die with string values and the name “spite”, and the expression will roll add that to the roll instead, that’s what I’ve done here:

This way you still have to roll each side separately but it can be adapted for a combined roll where each side’s dice pool spawns a different string value die on the sixes.

I know it’s a little convoluted but I hope it helps :)

Update: I thought about it a moment longer and if you want simplified expressions you can make specific dice for each side, with an expression on the faces you want to count up spite like so: