Flat Speaker Cables

Second the Alpha Core Goertz. Make sure you get the zobels if you buy them.

Your post is technically curious; "under hardwood floors"? Or, do you mean under carpeting? If it's going under the hardwood flooring you don't need flat cable. I'm thinking that you wouldn't want to put the cable between the subfoor and wooden floor, unless there's some construction techniques that I'm unaware of. Unless it's some kind of Pergo floor where the cable could be with the foam underlay... Seems like making more work than benefit.

There are also faux moldings which can hide cabling along walls. An alternative option if you don't want to go through the floor.

If you still need flat cabling, Audioquest has some flat cables. Ultra Fidelis is an Audioquest dealer near me and would know: 414-221-0200

I'm not sure about the Magnan cabling for that purpose. I'm reviewing them right now. I would speak with Dave at Magnan first before attempting this. It's a very thin, wide cable but I suspect he may say it's not intended for use under carpeting etc. The reason I say this is the dialectic/jacket is quite different from the others mentioned and the thinness of the cable may be problematic if it's to take foot pressure on it. Magnan's number is:
805-484-9544

Hey,

I own a pair myself, it only uses std OFC 14AWG copper cable internally, nothing special. so don't buy expensive cables, they don't do anything.

Morrow SP1

Wow, under hard wood floor? I'm curious how the speaker cables would stay unharm underneat and what they look like when they "raise" above the surface?

Anyways, the Goertz Alpha-Core is narrower in width but thicker & harder material than any of the Nordost and would be almost impossible if bending SHARPLY at 90° (vertically) while the Nordost FlatLine can without stress.
However, if it'll be under heavy traffic, I think the Goertz can withstand better.
Keep us posted.