Multiple amps, through different combinations of cabs, sometimes using a 2, 3, or 4 way splitter to feed them simultaneously, sometimes with different mics or combinations of mics on each cab. And change up the guitar too, if not something like rolling back the volume and coil tapping a pickup. Sometimes the purpose is width, sometimes its density.
Even when you have several amps layered up, I overdub anyway. So for example, you could have a Matchless, Badcat, Marshall blend happening on the left side, with a Fender, Budda, DrZ blend going right as a second take.
Another approach is what @SoundCandy said. One primary amp, the others color the primary. So if the Matchless is the main amp, but its lacking crunch, pull the Budda, mids all the way up, lows fully attenuated. Highs adjusted as needed. Or say you love the clarity and punch in a wall of sound from a JCM2000 but it lacks sparkle and chime. Then toss an a Vox, Divided by, or 65 amps unit to add what its missing.
Here's another trick. Remember that very few amps actually cut or boost. Most of these, you're opening and closing a HP/LP filter. Others, your tone controls cut in different ranges. But they do not boost. So when you're changing the dial on the mids, all you're doing is sweeping around with a one band equalizer in a limited range below zero. Some amps have presence knobs which can be high shelf.