There are stereo guitar amps.
Leaving that aside, many guitar amps are deliberately designed to induce distortion of the guitar signal when overdriven, especially if it is a tube amp. Solid state amps often attempt to emulate that overdriven distortion sound. Guitar signal distortion can sound cool, and it is a familiar tone to most rock fans. This is precisely the opposite of what you strive to do in home or portable audio for critical listening. You strive to find an amp that will reproduce your recorded music accurately. Distortion is by definition not reproducing the input signal accurately.
In summary,
1) guitar signal distortion by amp = pleasant for many of us
2) DAP or home audio source signal distortion by amp = bad sounding.
Don't use a guitar amp for driving headphones while listening to a home or portable audio source. BTW, your little Danelectro is fun, but there's no way that will reproduce music accurately. It will sound like crap through that amp. I have a mini Fender that is about the same size, and it's fun, but it's mostly a toy to fool around with, or sometimes a cute little travel amp that packs easily for practice when away from home. That's it.