Sub wiring help, high level speaker terminal to RCA line level Sub inputs

Use a Paradigm X-20 crossover if you can find one used. Speaker level in - RCA out. Phase, frequency, and level control included.

Here is the actual LOC circuit along with a very succinct explanation
http://www.epanorama.net/circuits/speaker_to_line.html

Study it. This is exactly what I did. It was worth it to me to install this circuit- really nothing more than 2 resistors and one short length of wire per channel- inside my amp. It is however a very simple circuit. Keep in mind it does not matter at all where this circuit is located. When you buy a sub with speaker level inputs the exact same circuit will be used only inside the sub. 

Also like the above link explains these are 1/4 watt resistors. They can be so small because hardly any power goes through them. Regardless of volume. Regardless of your amps power. Regardless of how much you turn it up. The difference between one LOC made for high power and one for lower power is not the resistor wattage. Its the resistor value. The 10k resistor isn't used to pass power. Its used to attenuate. A bigger amp would use a 20k or greater resistor, but it would be the same 1/4 watt value.

What this means, being so small, no heat output, you can put it anywhere. You could practically wire it into an interconnect if you wanted.

Also the parts are like $2. Total. Quality just does not matter. It might if you were using it to listen to the full range signal. In this case though, low bass only, waste of money.

How you do this depends on a lot of things I just can't know. What you like the looks of, for example. What interconnects you're using. What you may or may not be comfortable soldering or modding. You could for example very easily remove the RCA from the end of one interconnect, solder the resistors, and attach the wires at the end to your amps speaker binding posts. Direct from the speaker outs to your RCA ins.

That one link above, just the one page, contains a wealth of information. You just have to figure out your best way of making use of it. I did, and mine works and looks just as good as any professionally built component. Yours can too. You just have to decide how you want to do it. Heluva lot less work than boxing and shipping. Lot more satisfying too.

@millercarbon Thanks that's a lot of good info, I'll read up on it more closely, seems like real easy job. I ended up buying the Y-splitter to see how that works out in the mean time. I could already use some cheap stock rca's I have laying around to try out the resistors.

A Y-splitter coming out of the pre-amp to connect the amp and the sub will probably work just fine. Doing it that way the pre-amp will see the input impedance of the sub and amp. Where now it sees only the amp. Should not matter but not knowing any of those its impossible to know in advance. The bigger concern I would have, and still not much but it is bigger, is this puts a splitter in the signal path to the amp. More to the point, it puts an additional connection in the signal path. No matter how high quality a splitter you get, or how great the connection, there simply is no getting around the fact you're degrading the signal. Whereas using the power amp speaker path leaves your signal path pristine, untouched.

Frankly this is probably more a theoretical than practical concern. In all reality you will probably never hear the difference. But it will be there. That for me is enough to not even want to try, and is why I suggested the LOC instead.

I completely agree, that's the main reason I didn't want to go with any kind of adapter/splitter and just figure out some way to get a direct connection. It bugs me to spend money on better speaker cables and then terminate them with a Y-splitter.

Just for discussion using the resistors, is it possible to get unwanted feedback back into the pre-amp that can cause some other kind of distortion?