Mr. stevecham
I would like to clear this subject:
This thread is about speaker cables.
Your (all of you) system is a given. I have nothing to do with your choice of equipment.
The idea of speaker cables to fit the DF has no significance when tube amplification with very low DF is involved. So is your case. There were other guys who asked me, with tubes, I've told them the same and they accepted. Please do too.
If such case occur (low DF), it is not me to say it is not working for that, it is the math behind the idea. As much as it works for high DF, it is not working for the low DF.
The speakers are not much of a player in this game. Unless, they are not conventional. Even thou, in the case of Mr. keppertup it worked very well.
I think that the name: "speaker cables" are a mistake. They should be called amplifier cables!
I do not want to get personal in this thread. Except a few guys who need their daily dose of contemning my thread, for quite a while, all other are welcome.
Speakers sensitivity or efficiency: The range goes from the highest (106dB/w/m SPL) to the lowest (85dB/w/m SPL). There might be exceptions, but this is the majority.
The combination of 88dB/w/m SPL sensitivity with low impedance of 2.7 Ohms, makes the Thile a taught cocky to drive.
Understanding Damping Factor and its role in the chain of amplification, cables and speakers:
If I would reflect the audio world into the car's world, the amplifier would be the engine. The speakers would be the wheels. For the power (watts) would be the engines HP. The DF is the engines torque.
The speaker cables would be the driveshaft.
We know that an engine with lots of HP but low torque will not deliver the sporty drive experience. A powerful engine must have both: the high HP and a high torque.
The fact, that tube amplification has a problem with DF is an old issue, that been tackled by SS. It is even better with class D but in a different way, not as with class A/B amplifiers.
Speaker cables as drive shaft, would present a serial device with some flexibility to be the extension of the amp's DF. A thin cable would be more flexible, and a thick one more rigid. Why would someone like to get a car with a strong engine with fantastic torque and than ruin it with a thin (flexible) driveshaft? To deliver the power from the engine to the wheels with a high torque engine is like delivering the power of an amplifier to the speakers from a high DF amplifier. It is about control! The high DF is more control. A coil loaded speaker requires such control, to overcome the reactive nature of a moving coil in a magnetic field (speaker structure).
That's the analogy. I hope it helped some to better understand it.
This relation is not an empiric figure to guess of find by trial. It is a figure that has values and can be calculated. The calculation is telling with accuracy, what is the required cable for the task.
Regarding your system, did you try some other combinations like matching a very efficient and easy to drive, horn loaded speaker with your Manelly?
Did you try a powerful SS amp with high DF and thick cables attached to your Thile?
Even if you did, and you like your sound, that's O.k. My remarks were pure technical.