Wiring a subwoofer to monoblocks

Just picked up a REL Quake
REL's manual speaks about differential amps – does this mean
Mono blocks?
No friggin idea how to wire it up.
My i/c’s are fibre optics which break the ground between boxes so wiring the earth to the pre is no use.
To make matters worse, the Audiopax reverse polarity /phase.
Have mailed REL but no reply.

When the manual speaks about wiring to the chassis ground,
How do I check this?

Next problem will be a plan to use two subs and I'm not any clearer from their manual how this will be achieved.

I have spare pre outs on the Supratek but would prefer to run the the sub/s using the hi level inputs.
PS Audio HCA-2: I sent a request on their tech support forum and was told by Paul McGowan who responded to the post to install a 1Kohm resistor in line with the black wire and the negative speaker terminal (I had tried the Ayre chassis screw trick and it did not work).
Good info, and a clever solution if connecting black to chassis does not work (which I think would mean that on that amp chassis is not common with circuit ground).

If that proves to be necessary, with a 30W amp I'd suggest that the 1K resistor be rated for 1 watt (or more), to be sure that the resistor will not be overheated if the amp is putting out high power for significant time AND if a connection somehow exists (now or in the future) between sub ground and amp ground (which would result in significant current flowing through the resistor).

-- Al
When I had a Rel for the front I connected the Left and right to their terminals, then I connected the common to the preamp. When I tried it to one of the amps I got a loud hum and did not when I connected to the ground tempinal on the preamp.
Thanks all,
I do not believe the Audiopax are balanced.
As the spec it's two 15 watt amps wired in series to give 30
so I should be ok.
I've seen the resistor idea before.
I'll not be rushing into this in any case, says he feeling
impatience gnawing at his leg:_)
Has brought about some polarisation of ideas on one of the uk sites as some people reckon valve amps (some anyway) can't drive subwoofers/or do bass so the low level input to the sub is the way to go?
I was hoping that the 100 watt amp in the sub would take a bit of a load of the 30 watt amps trying to drive 4 Ohm speakers.
My only experince of subs was a large REL Stentor when I was using a Passlabs X-250. I loved it finding it hard to beleive how much it helped across the spectrum.
Then the wife kicked me out of the lounge into my wee cave
and the Pass and the REL were serious overkill:_(
With my Monoblocks and one REL subwoofer, I have one hot wire (red) to the + speaker post of one amp. The other hot wire(Yellow) to the + speaker post of the other amp. And the ground (black) to the - speaker post of one of the amps (either will do) Sounds great!
I do not believe the Audiopax are balanced.
As the spec it's two 15 watt amps wired in series to give 30
so I should be ok.
I suspect that is not correct, Simon. It may or may not be balanced in the sense of processing out-of-phase differential signals through its internal signal path, but the fact that the secondaries of its two output transformers are apparently wired in series tells me that the two output terminals are most likely balanced (with neither being at ground potential).

In any event, as I indicated above, no harm can come from trying it with sub black connected to amp chassis (or to preamp chassis, as Hevac suggested). Just don't connect sub black to amp black unless you are totally certain that amp black does not have a signal on it.

-- Al