I used to do a kinda similar trick recording rock guitar: two different mics on the cab (usually one dynamic one condenser) and double track. That way I got four tracks total: take A mic 1, take A mic 2, take B mic 1, take B mic 2 and then I would pan A1 and B2 hard left and B1 and A2 hard right. Feels like four guitars, but without phase issues on either side. You could just do the same with different IRs and get an even more pronounced effect.
I didn't consider actually using different impulse responses, I'll definitely give that a go. And while I have listened to some argent metal, I never actually thought about using a synth for the sub-bass instead of an actual instrument or an octaver plugin.
Thanks for the tips, I'll definitely enhance my repertoire with your suggestions.