I don't know if it helps, it's just a camera recording afterall, but it's very clear how this doesn't sound like the defaults we have on MAME. Bass and synths are clearly audible, drums are not remotely nearly as loud.
Why this is? No idea. Maybe the arcades passed through some kind of standard sound level tweaking before being sent to the buyers, who knows? All machines I heard in my life sounded like the one in this video. I'd guess it's not MAME's fault, though. Sound channel levels are configurable in MK1 and MAME defaults them at... default. But it's not how it sounded in the arcades, I tell you.
Edit: (I love Google) Full arcade soundtrack in MP3. Compare The Courtyard's and Goro's Lair's songs with those in the test switch's sound board test. This is what I'm talking about.