equating class A to class AB SS amps?

A watt is a watt is a watt. It costs a lot more to build a pure class A amp than a class AB amp of the same power. Class A amps are very inefficient, need large transformers (power and output, if applicable), and dissipate a lot of heat.

For all their disadvantages, Class A amps often have a kind of liquidity that is hard to find in Class AB designs.

Class A amps go into clipping more gracefully than class AB amps. This sometimes leads users to push the class A amp hard into a load because of the gradual move into distortion (and largely 2nd harmonic distortion at first, which is pleasing to the ear).

So the L-509u is capable of much more power than the L-590Aii. There is one more factor to consider, though, and that is how the two amps behave as the load impedance changes. Speaker impedance often varies across the frequency spectrum, and it's not clear how well the two amps deliver current to lower impedances. Class A amps often but not always have an edge here due to their large power supplies and basic topology.

If you are using efficient speakers consider the L-590Aii. It will emphasize finesse over brute force.

An amplifier is a tool to drive your speakers, select them first and the select an appropriate one that you like the sound of on THAT speaker. There are many factors involved, ghostrider has pointed several of them out. Generalizations about the qualities of Class A, Class B, Tubes etc. are less important than the qualities of a particular amp and how well it matches your speaker.

Big watts.. little tiny watts. Tubes have BIG watts... Class A amps usually have BIG watts because they have big power supplies..
Cheap class AB amps have little tiny watts, unless they are BIG, really BIG (and expensive).. and can double the wattage with halving the impedence. (Think Bryston 28B-SST*)
But really a Watt is a Watt. (though some small amps cheat and claim they have more: that is the 'little' watt side of the story.
Really a 50 watt amp only puts out 50 watts into 8 ohms, and a 200 watt amp puts out 200 watts into 8 ohms. BUT!! that 50 watt amp may put out 100 watts into 4 ohms and 200 watts into 2 ohms.. (a few such heroic amps can do 400 watts into 1 ohm) but the 200 watt into 8 ohm amp may only put out 250 watts into 4 ohms and actually fizzle to less than 100 watts into 2 ohms, and explode (blow the fuses) when it sees a 1 ohm load.
This is only to confuse you as the power handling ind low imepdence loads has NOTHING to do with class "A" or class AB
However it all fits into the big picture of how power amps are rated.