strange rel subwoofer cable phenomenon

I've been using a Rel Storm III sub hooked up both ways (sunfire theatre grand II to the rel for .1 and bryston amp to the rel for 2-channel). I've been using a cheap interconnect for the .1 track (Ultralink Subsonix) and decided to give some higher end cables a try. The Cable Company sent me some Synergistic Research interconnects (one at $350 and one at $550). I like the brand and have the Kaleidoscope Phase II DAC-Pre and Pre-Amp after extensive testing. However, in this application I literally could not hear a difference between any of the 3. I heard only a tiny degradation when I tried the thin plastic cables that come with most popular-brand equipment. Is there something wrong with my ears or is this sub cable-proof? Anyone else out there found this to be true? I've been told that both XLO and Synergistic make neutrik connectors that will make a huge difference for the Rel, but now I'm not so sure...
I have found that interconnects usually make most difference at higher frequencies, as one would expect since it is the capacitance that is the key design parameter for interconnects, and the effects of capacitance are proportional to the frequency. Since the sub isn't carrying high frequency information you won't hear the difference.

The neutrik connection to the subwoofer is electrically quite different from the RCA connection so I'm not sure that you can infer from one to the other. However the neutrik connection is also from a very low source impedance (speaker terminals at the amp) to a very high input impedance (the REL input is really a voltage sensor). For this reason I would not expect a marked improvement from using expensive speaker wire, and I would even go as far as to say that speaker wire is the wrong wire to be using for the neutrik connection, since the connection to the REL is carrying virtually no current. It is probably better to use a low guage (say 24) PTFE insulated wire, not braided, to minimize the capacitive load on the amplifier.

Having said all of that the proof is in the listening, so if you have can demo the cables then give it a try and let us know what you find.
Not to worry. In objective tests most people cannot tell the difference. You're being objective, you're listening. So much (incorrect) hype and BS about wire. Save your money and enjoy.
I don't think it much matters if you can't hear the difference. Isn't that the ultimate test? I trust your judgement more than my experience- after all, your ears are in the room. One caveat- don't listen to those who say cables don't matter. They do. Luckily my wife has great ears and can hear the difference too. When I upgraded to Siltech she heard a big difference. The previous upgrade to Synergistic Research had been a big disappointment. A lot has to do with your gear. One nice thing about Audiogon, is that you can try a lot of things cheaply.
I bought a cheap cable from Best Buy for my Stadium IIIs and replaced my Cardas Hexlink with it. I didn't hear any difference in the sub. Sold the Hexlink and pocketed the difference. On the other hand, I went from Cardas NR to Nirvana X-S between my preamp and amps and noticed a large difference.
Oh yeah- I meant the cable upgrade from cd to pre-amp and pre-amp to amp made a difference ( I upgrade both pairs at once). My speakers have a built in sub, so I don't use one.
I have replaced my Rel Neutrik cable with Signal Neutrik Cables and found out that the Rel is sounding much deeper. Try them. There is money back gurantee.
I myself have a Rel Stadium III sub, I have hooked it up both ways, and did not notice a ton of difference from interconnect to interconnect, however I have "built" my own neutirk connector, and noticed more refinement and clarity. I used teflon coated wire (silver plated copper) of 18 gauge, made the over all connector lentgh the exact same as my speaker cables, and I put some banna plugs on the ends that connect to the back of my amp, and swapped the neutrik off of Rel's cable and put it on mine. The wholel project cost me 25 to 30 bucks worth of parts, and it was worth it in my opinion, not to mention it was also fun. And like I said, as far as interconnects go, I have had el'cheapo's hooked up, and I also tried a set of transparent cables for grins and giggles, didn't really notice enough difference to warrant the hundreds extra that needed to be spent. If you would like some instructions on how to make your own neutrik feel free to email me and I can send you a parts list and easy to follow steps. Have a good one.