Here's my useless answer. I have no clue why a solid state amp would have different outputs for different speaker impedances. Tube amps use a transformer to make the tubes "see" the right impedance to keep them linear and non distorting to the highest levels possible, and multitap transformers are common in tube amps. Solid state amps, as far as I have seen, just don't care what the imipedance of the attached speakers may be, until that impedance gets low enough that the amp will overheat when driving the impedance hard. But typically a solid state amp that is specified to be able to handle a 2 ohm load uses the same outputs for a 2 ohm load as for a 16 ohm load. Thus my cluelessness.