Does anyone care to ask an amplifier designer a technical question? My door is open.

Ok, what would be the difference if they are isolated vs not isolated...would this have changed the way the amp behaved...or I guess the right side speaker? 

@Daveyf, what model are the speakers and what model is the sub? Also...

I also have a REL sub hooked up to the amp, it is left, right and ground at the amp, as both the amp and the REL are balanced designs.

I presume you are using a three-wire cable to connect the sub’s Speakon connector to the outputs of the amp. Does "ground at the amp" mean that the ground (black) wire in the cable is connected to the amp’s chassis, or to a terminal that may be provided on the amp as a means of connecting to its circuit ground, or does it mean that the ground wire is connected to one of the negative output terminals of the balanced amp? And if the latter, is the ground wire connected to the negative terminal of the channel that produced sound when you misconnected the wires, or to the negative terminal of the channel that didn’t produce sound?

Regards,
-- Al

Al, the ground wire(black) of the sub is connected to the ground lug on the amp chassis. Rel T5i sub and Sonus Faber Guarneri Homage speakers. The sub is connected with a three wire connection. Left, right and ground. 

@Daveyf, thanks for providing the additional info.

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

Thanks, Al. I think that given that I had the cables crossed only at the speaker end...the amp end was wired correctly, that it is unlikely that the amp was connected as in your last paragraph. What I don’t understand, is why the right channel was playing and not the left.No signal to the left whatsoever! Only once i corrected the cabling connection error did the sound return to the left speaker...and all seemed fine.
OTOH, perhaps I hadn’t noticed if one speaker ( the left) was hooked up the way you describe in the last paragraph, Hmm.