I really don't use the 990's for anything since getting the X1. They are awesome for immersive gaming and music. Lately I've been listening to a lot of modern jazz (aggressive bass and drums) and dubstep, both of which sound great. For classical, I prefer my Sennheisers, for a more natural and neutral sound, so it can depend on what you like to listen to. The SB Z puts out a really nice clear sound and has some great processing available. Really, I don't think you can go wrong with the Z + X1.
Damn, so you been using the X1 over the 990 since u got the X1? The X1 is really that good over the 990 Pro?