Bullethead - In this case it seems as though the problem is getting the audio to play out of the sequencer. I had no idea it was even supposed to do so, but now I at least know I don't need peripheral speakers. So now I just need to figure out why the sequencer isn't playing anything at all...
Hmmm. Well, there are several things you can check here to try to get it working.
#1. Make sure the sequencer is a stand-alone piece of scenery, not part of a building. You can only change the sequencer's music if it's a stand-alone piece of scenery. Once you've got the music you want, you can then move the sequencer and attach it to a building if you want, and the changes you made will carry over.
#2. To actually change the music of anything (not just sequencers) these days, it's a 2-step process. First, you have to select the song you want off the menu. Then you have to hit the OK button down at the bottom of the menu. If you don't hit OK, the song will be highlighted and look like you selected it, but actually you haven't so the changes don't take effect.
#3. The sequencer's music is like flat ride music. It starts when the sequencer itself is activated, broadcasts out 360^ from the sequencer part itself, and ends when the sequener's finished all its triggers. So, to hear the music, first you have to be close enough to the sequencer, and then the sequencer has to be activated. The activation can come from a trigger somewhere else, the time of day, or you hitting the PLAY button on the sequencer.
#4. To reiterate, the display speakers that you link to the sequencer simply parrot the sequencer's own music. So they also start playing when the sequencer is activated.
So.... Here's what I suggest. Taking the above things into consideration, set up a sequencer to play one of the stock songs. Hit its PLAY button and see if you hear the music. If that works, change it to your custom audio file. If that doesn't work, then you know it's a problem with your file. If it works, then you must have made one of the mistakes above, such as not hitting the OK button (that's my main problem right now--not used to having to do that).