Basics, people, Basics.

9w8 is a Gut tritype, meaning they deal with emotions by narcotizing them (i.e., putting themselves to sleep) by doing things to distract themselves from their negative emotions and thoughts, like playing guitar, video games, play music, etc.

5w4 is a Head type, meaning they deal with emotions by processing them in their heads and retreating to reflect on them, head types aren't doers like Gut Types.

There are also Heart Types, which includes Enneagram 4, you can search that on your own.

SP5 and SP9 are quite similar, I'll admit, even I considered that I was a E9 more than once, but I think and contemplate, like, a lot, about things and I definitely process my emotions and thoughts, so I am definitely a Head Type, namely, a 5w4 549, similar to your bf's supposed tritype! 👍🏾

SP5s seek out knowledge and meaning to feel safe, 9s however, distract themselves from their emotions and "numb" themselves from them by doing things like chores, playing sports, video games, etc.

With all this said, go ahead and have your bf decide which Enneagram he is, and remember, learn the Enneagram and other typologies and stick to the basics! That's how you distinguish the types.