How to wire my REL T7 to Audioengine A5's

Don't know how to use the Neutrik Speakon cable to the A5's
Do I hook it up on the left powered side of the monitor,or use
Both speakers?
I'm not sure you can do what you are trying to do. The REL Speakon inputs are designed to take signal from your power amplifier. Since the A5's are active, the only signal you can access external to them is the line-level out from your source, which probably won't be enough for the REL. Or I could be completely wrong. :-)
The spec's do not show the REL having any outputs. What is your source?

BTW if the Speakon was an output you would still need a speaker level to low level adapter.
Ideally you would want to connect the Speakon cable to both output channels of the power amplifier, which the sub would then sum together. However, since the power amplifier of the A5 is built in to the left speaker, there is no means of accessing the left channel amplifier output.

An additional constraint is that the only line-level inputs provided by the sub are an LFE input and a single-channel input for a full-range signal.

So assuming that the sub's LFE input would not be a suitable choice for use with your system, there only two possible ways that occur to me to get both channels into the sub. The first would be to get a mixer that would combine line-level L & R signals, and input them to the sub's single line-level input channel. The second is that if you are using a preamplifier or other upstream component which provides two pairs of INDIVIDUALLY BUFFERED volume controlled output jacks, you could combine the two channels of one of those pairs with a y-adapter.

Assuming that none of those approaches are viable, you would have to use the sub with only one channel being provided to it. That is not ideal, but may provide good enough results for your purposes.

To do that, connect both the yellow and red Speakon wires to the + (red) terminal of either speaker, and the black Speakon wire to the - (black) terminal of that same speaker. Or, alternatively, just connect EITHER the yellow or red wire to the + terminal of either speaker, and the black wire to the - terminal of that speaker, and don't connect the other wire. If you do it that way, the end of the unconnected wire should be covered with electrical tape, to prevent it from coming in contact with anything. Connecting all of the wires is preferable, though, as it would have less susceptibility to the possibility of noise and hum problems.

-- Al
Wow. Got a lot of options here. Humm. Guess ill try
Using what I have to work with ATM. I didn't want to
Blow my lil starter of a system up before I got y'all's
Opinion first. Guess ill give Almarg method a try first.
Oh I have a Audioengine A1 DAC if that helps with
My system to be Properly hooked up. The DAC is
Connected to my X-Fi Titanium HD OPT out to the
A1 OPT input. There is another OPT in on the
Titanium HD if that helps. Thanks 4 all the Support.
Couldn't find any info on a model A1 DAC, and I presume the DAC is not the currently manufactured D1 model, since that doesn't have a coaxial S/PDIF input.

In any event, I would assume that the DAC doesn't provide two pairs of independently buffered outputs, so, yes, go with the method of connecting to one speaker. I suspect the results will be satisfactory once you finish optimizing the control settings on the sub.

-- Al