How is the Speakon connector wired for REL sub?

Tim, according to several references that I found the speaker-level outputs of your Primare A30.1 are balanced, meaning that both the + and - output terminals have signals on them (as opposed to the - terminal being connected to ground in the amplifier).

Therefore you absolutely should not connect 1- or 2- to either of the - output terminals on the amp. If you were to do so you would risk shorting the signal on the - output terminal of the amp to ground, thereby damaging the amp (at worst), or triggering its self-protective shutdown mechanisms or blowing a fuse (at best).

The problem would occur if the amp and the sub both have 3-prong power plugs, and both components have ac safety ground and circuit ground connected together (as is commonly the case). In that situation a path would exist from the amp's - output terminal through the sub's internal ground to ac safety ground, then through the ac safety ground wiring back to the amp's internal circuit ground, resulting essentially in a dead short between the amp's - output terminal and amp ground.

What you should do is to connect sub - to the ground terminal on the back of the amp, or alternatively to a screw on the chassis.

Regards,
-- Al

Can I check the amp's negative terminals for continuity to ground with a meter? Or check for continuity between the negative terminals?

I was about to post the following response when I saw your subsequent post, which makes this no longer relevant. But I'm submitting it anyway, as an fyi:

I'd feel very confident that doing either of those things won't hurt anything, but I'm hesitant to say that with 100.00% confidence.

What you could do instead, as a temporary connection arrangement to confirm that signals are present on the amp's - output terminals, would be to connect the + inputs of the sub to the - terminals of the amp (for each channel), and one of the - inputs of the sub to the ground screw on the back of the amp. If you hear sound from the sub with those connections, it would confirm that signals are present on the amp's - output terminals.

Best regards,
-- Al