Sounds good re the connections of the REL sub. You have NOT made the mistake I’ve seen more than a few members here describe having made, in which the ground wires of REL subs have been connected to a negative output terminal of an amp having balanced or bridged outputs. Which depending on the internal grounding configuration of the sub and the amp may often work ok, but depending on those factors risks the possibility of hum, sonic degradation, or even damage to the sub or the amp.
Given that, I think we can rule out the presence of the sub as contributing to the consequences of the miswire at the speaker terminals.
Also, while I couldn’t find a manual for the Sonus Faber Guarneri Homage speakers, I found a couple of indications that they are suitable for biamping, including this statement by no less than Martin Colloms in a 1994 review in Stereophile:
The filters are nominally 6dB/octave over the crossover range, augmented by additional components to shape the acoustic output. The treble high-pass section thus has three elements: two film capacitors and an air-core shunt inductor. For the woofer’s low-pass section, the primary element is a large series air-core inductor with an RC Zobel network and an additional film capacitor. The multi-way binding posts allow for normal and bi-wiring, or even bi-amping.I would conclude from this and from user comments I found elsewhere that it is a near certainty that the high and low frequency sections of the speaker are not interconnected in any way.
Given that, I don’t see how the miswire you described could have resulted in damage to anything. I would have expected the result to be that both speakers would have played, but with poor sonics as a result of the high and low frequency sections being driven with opposite polarity signals. I can’t explain at this point why one speaker would have produced no sound, assuming there weren’t any loose connections. But perhaps Ralph or Roger will have some further thoughts as a result of the additional information.
In saying this, btw, I’m interpreting your statement that the misconnection at the speakers that involved "one positive cable on positive, one negative cable on positive, one negative cable on negative, one positive cable on negative" did NOT mean that the positive amp output was connected to both + and - of the SAME section of the speaker, and did NOT mean that the negative amp output was connected to both + and - of the SAME section of the speaker. In that situation no sound would have been heard at all, from any speaker or speakers that would have been connected that way. Although again, even in that case no damage would have resulted to anything.
Best regards,
-- Al