I think if Gregorian chant is a kind of music you're accustomed to, then I say have at it. IME music that tends to be pleasant to your psyche when sober will often make good journeying music, with perhaps a couple exceptions. I think people get too hung up on either the traditional end of the spectrum (listening to icaros) or the electronic end of the spectrum (listening to psytrance and whatnot) and I do know first hand that they can have some pretty interesting and desirable effects, but if they're not the kind of thing you would listen to sober, there is a chance you'd find it just as boring in hyperspace as you do on land.
I think there are three qualities in the music you should keep an extra eye out for at that is sober preference (as discussed above), groove (which Gregorian chant lacks, but that's ok), intricate detail (while I personally may not be a big fan of electronic music, it does often pack textural detail and groove) as well as the harmonic or vibrational quality of the song. As you noted vibration is very important, and I would go so far as to say that it's the "name of the game". It seems to be at the core of hyperspace's system of physics. So much of the journey can be directly impacted based on the manipulation of vibration. You may not be able to fulfill all the qualities above in a single song or a single kind of music, but that's ok.
"Science without religion is lame. Religion without science is blind" - Albert Einstein
"The Mighty One appears, the horizon shines. Atum appears on the smell of his censing, the Sunshine- god has risen in the sky, the Mansion of the pyramidion is in joy and all its inmates are assembled, a voice calls out within the shrine, shouting reverberates around the Netherworld." - Egyptian Book of the Dead
"Man fears time, but time fears the Pyramids" - 9th century Arab proverb