How to go from RCA to XLR?

Although unfortunately there are variations, the most common xlr pin connection arrangement is:

Pin 2 -- hot (the positive waveform if differential [balanced] signals are being sent from xlr outputs)
Pin 3 -- cold (the negative or inverse waveform if differential signals are being sent from xlr outputs)
Pin 1 -- ground

If that is the configuration of your monoblock inputs, the center pin of the rca connector at the other end should be wired to pin 2, and the rca shell (ground) at the other end should be wired to pins 1 and 3.

To verify the pinouts used on the xlr's on the amps, you could either try to obtain a schematic, or perhaps some Googling would lead you to the answer, or else use a multimeter to check for continuity between pin 1 and signal ground on the amp (probably the chassis).

Verifying the ground pin is key. Reversing hot and cold (usually pins 2 and 3) will reverse absolute phase but will not hurt anything. The sonic effects of absolute phase reversal would be subtle, and would be correctable by changing plus and minus connections to the speakers, as well as by having correspondingly reversed connections in the xlr to rca cable.

Regards,
-- Al

Great answer, Al. Thank you very much.
Could I use the "ground prong" (the round "3rd" prong) on the power cord's plug to check for continuity with the ground pin on the XLR input?
Scott

I'd suspect so, but I'm not sure that would necessarily be true with all equipment. Try it and see. If you get continuity to one of the xlr pins, you've verified that that pin is ground. If you don't get continuity to any pins, then that approach won't provide you with an answer. Same goes for measuring to chassis.

By "continuity" I mean something very close to 0 ohms (or at most say 1 or 2 ohms), as measured on an ohmmeter, not just an indication from a buzzer or other rough continuity checker which could indicate continuity even if a significant resistance is present.

Also, when you measure it would be prudent to have all signal cables from other pieces of equipment disconnected from the amp, so that your measurement is not confused by any possible paths to ground through the other equipment.

Regards,
-- Al

The standard for US equipment is pin 2 hot. Europe and most japanese brands use pin 3 as hot. It really doesn't do anything but reverse phase if it is not same, as Al stated.