Thanks for the suggestion, unfortunately it didn't help. I'm currently working with the tracks in the picture below, trying to figure things out. The top track is the midi track I imported, and as you can see, the midi track is routed to the instrument track, which has ASIO4All as the output. At this point, I don't get sound from any of it. When I play the track there is no sound, and when I open the instrument properties (this picture of the bass guitar) there is no sound when I click the strings.
So now I just replaced the synth in the instrument track, setting it back to SI-Bass Guitar again, and everything works. I can open the SI-Bass Guitar properties and get sound when I click the strings. And when I play the track there's sound as well. It works, but I feel like I just stumbled into a solution. It seems I've had it working like this before, but then I bring in a new track or something and it stops working. My understanding of how all this works is so lacking it's all trial and error, and when I can finally get it to work, I have no clue why it works.