Wiim's answer from Dec. 2023 did not assume that all four speakers "stay at 8 ohm." Their guidance was quite clear: powering nominally 8 ohm speakers in parallel (ie, four speakers in total) is OK and should not present any problems for the Amp, essentially because a pair of nominally 8 ohm speakers in parallel is an equivalent load to a single nominal 4 ohm speaker. Powering nominally 4 ohm speakers is parallel was discouraged, because the result is a nominal 2 ohm load, which can present problems to the amp.
Its common knowledge that an "8 ohm speaker" will present load impedances below 8 ohms in portions of the frequency range, typically minimums in the 6 ohm range or even lower. Similar with 4 ohm speakers, which commonly present loads in 3.2 ohm range. Wiim is well aware of this and their "blessing" for powering four 8 ohm speakers does not presuppose that those speakers never fall below 8 ohms.
So I suggest your two take-aways be:
1) you should consider driving 4 speakers from one Amp or Amp Pro only if the speakers are relatively higher impedance eg nominal 8 ohm
2) the Amp and Amp Pro should have no meaningful differences in this regard. The PFFB circuit in the Pro mitigates frequency response variations across load impedance changes, but does not fundamentally change the ability (or inability) to drive low-impedance loads. The Amp Pro amplifier improvements (ie, PFFB) doesn't offer more power, or a larger power supply, or improved support for very low impedance loads. It simply offers lower noise and essentially load-independent frequency response.
fcc.report
fcc.report
