Damien, I am using Chord Crimson interconnects at the moment, although I haven't really experimented with this much, will get around to it one day
I must say, before I bought the GS10's, I did have a listen to the RS6's with Rotel amp & CD and I didn't really like the sound much.I expected it to be a warm sond, but it wasn't very tight. In fact, in general, I have found that stand mount speakers seem to be less sluggish. Indeed I would actually prefer to have floorstanders as I think they would look better in my home as they are a piece of furniture, however, I wasn't prepared for the trade-off in sound which I discovered. Of course, lots of people love the RS6's so this might just be a personal thing.
I must say, I dunno what the copper cable is that I used to Bi-wire the tweeters, it was some heavy copper cable I had had around for some time as it used to power my old tannoy speakers with Denon amp and Marantz CD50 set up from back in the 80's! - So sorry, I can't be of any help there, but I would suspect that any heavy copper cables would do a similar job. The cable has a lot of strands (over 50) and a clear insulation.
As far as warmth is concerned, I guess the standmounts are in general slightly less warm, however, a good pair of stands can certainly add warmth and things such as speaker positioning and room furnishings can do a lot to increase this, so I wouldn't worry about this. In actual fact the GS10's sounded a bit harsh in the shop, but when I got them home and set them up properly with the cable change mentioned, it was an entirely different story.