"So What?" by Miles Davis from Kind of Blue, from the bass intro through the ensemble section and well into Miles' first solo. It's an excellent test of balance across the frequency range, the tonal fidelity and acoustic space, all in a couple minutes. And if the system you're trying has the technical chops to cover those details, it should be capable of conveying just how funky a number this track is. Most stereos, including some really fine ones I've tried, tend to make it seem a little downtempo and mellow, but the rhythm section (Paul Chambers and Jimmy Cobb) are driving things like clockwork and the horn players capture that drive every time they blow; if the stereo's got any soul and you're not dead, you should be nodding your head to the beat before the time's up, or you're going to be left feeling a little unsatisfied and maybe can't put your finger on exactly why.