No. That’s not possible. Amplifiers can only be bridged in pairs, and pairs of pairs, etc. And if they’re not identical amps, you’re asking for trouble, too. Some stereo amplifiers are wired so that you can bridge the two “halves” to create a mono amplifier. I’m betting he has something like that. For example, I have a retro home audo system with two SAE A502 stereo amplifiers, each one bridged with itself to create two mono amplifiers. If I were so inclined, I could then bridge those two mono amplifiers together. Then I could buy two more and bridge them, and be able to create a minor earthquake! I’m betting that one or more of those three amps is also a 4-channel, and he’s bridging them in some odd way to create a balanced pair of pair of amps.