They sound pretty good together. The X5 is a bit bright and the UM2 is pretty dark, so the combo is fairly neutral overall, at least with the Shure Clear Flex tips. With the stock Comply tips, it's dark as hell, but you might actually prefer that with (c)rap and similar genres. Speaking of which, I don't listen to rap(e) but metal and rock is definitely pretty good with the UM2. It has a softer sound which will blunt the edges of electric guitars, and if the record is sibilant, the UM2 will not conceal that. Brighter sounding records can be pretty painful, but then again, they're even more painful on other IEM's, except the E5c, which is very smooth in that regard.
Anyway, the UM2 is probably the best universal fit IEM you could get for the X5, though if you want it to be really smooth, you can get the E5c instead, though you will take a slight hit in clarity.