I think you are right about optimum use. I have a quality old school Remote Preamp (B&K PT-3 Series II) on my main system and am using an Toslink DAC to feed TV sound to it, and Chromecast Audio for Streaming. Feeding the B&K outputs to the PW Amp Aux In should give me ARC, using it as a power amp, and an alternative to the CCA for streaming if that is more convenient. I understand that if you shut down the Play-Fi App the PW Amp defaults to the Aux input.
The Klipsch Powergate has definite advantages for use as an integrated controller with remote.
A third option, which for my use may have been a better choice, is the Paradigm PW Link. Preamp out only, no separate sub out, but it does have a Toslink Input and full ARC Room Correction. It is available now for $155ish on eBay. Simply looked at as a way to add room correction (including mic) to an existing pre/power amp system...that seems very very cheap.
The sister Brand Martin Logan has clone products, the Forte Amp & Unison Preamp, but both seem to be at their original $600 & $400 prices.