My friend, who is a drone enthusiast, has a few questions:

I’ve been thinking lately a lot about using a baritone 28" scale guitar tuned down to A D G C E A, which would be fed to polyphonic octave pedal (among others) to get an octave lower. Can an octave pedal go that low? Furthermore, are common guitar amps capable of going that low too? If not, is there something like a frequency splitter that would take low frequencies and feed it to a bass amp in order to have a parallel feed to a bass and a guitar amp? Just wanna know your opinions on this one.
It depends on if you want to play clean or distorted. most guitar amps will be able to handle it clean but it will sound like ass when it distorts. you can definitely do a frequency splitter.
Prs se Holcomb is the answer
Not that I've tried it, but I imagine you could use an A/B/Y-pedal, plug one output straight into a bass-amp and the other into an EQ-pedal and go to the guitar amp from there.

Many old-school guitar amps' gain-stages will actually pass all the low frequencies, even with the low A an octave down. However, like Min suggested, distortion will sound like arse a lot of times. Google "blocking distortion" if you care for the technical explanation.
Modern high-gain amps will often filter out very low frequencies because they aren't necessary for high-gain most of the time, and also to prevent the aforementioned blocking distortion.
Also consider speakers: most guitar speakers roll off below 100Hz or so, so they aren't capable of producing really low lows anyway. Even the mightly EVM-12L loaded into an 806 cab is no exception to this.

To be honest, even some bass-rigs won't be able to reproduce the fundamental frequency of the octave-dropped low A. For comparison: The lowest note on a standard-tuned 5-string bass is actually a whole tone higher than this. Whether or not this is a problem depends on the sound your friend is going for; thanks to psychoacoustics, people don't actually need to hear a fundamental to perceive it.
Maybe an amp intended for electric organs & synths?
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