In the absence of the KAESOP card, do the RJ45 connectors on the front of the K amps serve any purpose? Is a hub required in order to control several of the K series amps via RS485? Does the hub that Powersoft sells convert directly from USB to serial control, or must an additional converter be used?

Yes, a hub is required to talk to more than one amp via RS485. Our hub is serial all the way through, a USB-serial converter is still required.
The rest will depend on what you're up to. If you need emergency fault monitoring for the amp part, or - with a DSP inside - a preset change from time to time, then RS485 will do, I guess, simply because it's in the nature of the game that serial communication is pretty slow, especially with "several" amps.
The KAESOP Ethernet board will feel like rocket speed then. For serious work (as opposed to serial?

Greetings,
Thomas