Sex Mastery XQ core is for the custom subliminal and contains the core modules.
The Ultima are different product lines that are fast acting, which you could expect to see the effects within an hour or two. Best used when expecting to do something. In this case, if you were planning to have sexual intercourse, use the Ultima of Diamond, or Sex Mastery, or Libertine, True Social if planning to socialize, Sanguine Ultima for reconciliation/mood lifting and so on.
And then you have the SMX2 which contains many different modules aimed to make you a sex god.
You will come across some titles that would contain a combination of many titles, such as Primal Seduction, which contains Primal title, Sex and Seduction and Sex Mastery, among other extra goodies.
The suggested listening is a normal title and then supplementing it with an Ultima, in this case Sex Mastery and then the Ultima after a while. The reason behind this is that the normal titles have a long term effect compared to ultimas, although you could use an ultima like normal and still reap a lot of benefits. Furthermore, the normal titles usually contain healing while the ultima version of the same title would not; as it is expected that you’ve used the normal version. A more narrow and focused acting is what they are.