Try this: "Hey Siri, set your volume to ten percent."
Since Airplay is a lossless transmission, since I've had my HomePod I've been on a mad reripping jag, taking discs I'd previously ripped at 256KBs and reripping them losslessly. No compression on the rip and no compression on the transmission means I'm getting CD quality directly out of the speaker. For classical, with its huge dynamic range, that's a good thing. My lossless rip stack is edging toward
Also, while I'm nattering on, I use the Remote app that Apple makes and pair it with my iTunes-running machine. You can configure that to, among other things, give you a list of the composers in your iTunes library. Alas, what you'll discover is that, although it's getting better, Apple's classical metadata is not very consistent, does not use the Sort Composer tag, and you should expect "Ludwig van Beethoven" to be alphabetized under "L" not "B".
So if you're willing to spend time getting your metadata in order, iTunes + HomePod + the Remote app make a nice combination. I can pick up my iPad, scroll a list, touch i.e. Erik Satie, get an alphabetized list of his works (or at least, the ones I've ripped), and choose to play the one I want. And all it takes is an absolute eternity editing metadata, and making sure the machine that you're running iTunes from is not signed in to Apple Music in any way, because if so their metadata quite rudely elbows aside your metadata.