Yup, you're right. It is easy to test the "non-musical" sound. The most important thing is the "musical" stuff.
At midrange test, we know that the vocal not only should exist (which of course it does) but it should also be natural.
Now quality bass should also display natural "musical" sound.
I don't listen to pipe organ or electronic music but as a test I play the music for a special purpose such as healing, meditation, etc. This kind of material usually provides sub 20Hz sound. Most of the music will contain the sound of sea wave as it is the most common natural sound cotaining low frequency.
The good thing about this seawave recording (may be certain movie related to sea storm contains this low frequency too) is that you can hear the "soundstage", such that good speaker (box) will have natural sound while bad ones will have undefined "rumbling" of the low frequency.
The reasons I believe this album are quintessential in evaluating an entire system are:
the production is minimal; the quality of the production has never been questioned; the instruments are all acoustic; and the amount of detail heard and felt only increases as the audio system performance increases.
When "Blue" sounds good, everything else will fall right in line.
Solo strings are good test music, Cello goes down to ~60hz, Bass goes one octave lower to ~30hz. Fiddle and bass duo's make great test music as well as they present a large range and some pleasant sounding harmonics. Testing tones and sweeps are good for initial tests, but they don't reproduce the transient nature of music. I find the vibrato in cello great for demoing the resolution of system as well.
Zoe Keating is awesome for solo (ish, she layers multiple tracks of herself and there are other sounds present) cello, zo keating: music and projects, she has 3 albums streamed in their entirety at decent quality and available for cheap lossless download there. I like the middle of the 3 albums best.
For rock music open sounding duo's can be pretty good as well. Old Black Keys like the Rubber Factory album, "Dead Leaves on the Dirty Ground" by the White Stripes is pretty pretty open, with sparse but slamming application of kick drum (35hz primary if I remember right), I've used it to test power supply sag quite effectively.
As the poster above mentioned Kind of Blue, (other jazz quartets and sextets will be good as well) is awesome, though I find it hard to not get caught up in the music when trying to evaluate a certain aspect of the sound. For more Miles Davis try Round About Midnight as well.
What exactly do you mean testing bass?
Much of the bass you hear are the upper harmonics that have a lot to do with mids/highs and the crossover/phase integration.
Or are we talking about rumble?
Good luck listening to just a woofer or just a subwoofer. It will sound like mud.
My choice in bass is dual 15's run all the way up to 750hz, that setup has slam, like bass that hits you, and it can shake the walls also. It makes scary movies scarier, tactile impact bass, not just rumble. You feel the impact and rumble of an explosion. Much of the slam is also the fast clean leading edge of the notes coming out of the 1.4" compression driver also.
While fun, it doesn't hold a candle in the mids/highs to an 8" crossed to a round shallow horn crossed at 2khz. But that has more of a sub/sat sound due to lack of moving the air down below 200hz.
I like tron legacy, and most dance music from 10 years ago, I'm a sucker for the early now hits cd's.
The 35Hz centered dynamic wall-o-bass on "Angel" and the strong 17Hz sections on "Teardrop" have yet to fail in revealing weaknesses in my systems that will impact other somewhat less energetic music choices in more subtle ways.
Dean Peer has an album called Ucross. All fretless (I think) bass. The track Earth School is pretty amazing for dynamics and articulation. The tracks on the Sheffield Track Record (Amuseum and The Higher You Rise) are also pretty good.