Help me choice Audioquest speaker cables

Your dealer offering demo Redwood for $6k is far closer to a kick in the teeth than a favor. That model has been discontinued for at least a couple years, and is now highly depreciated on the used markets. The model above it, Wildwood (also long discontinued), is significantly better in ever way (twice the silver content, much better sound) and 6K is still way too much even for THAT model. 8ft Wildwood have gone used as low as low 2K recently. Dealer seems like he wants to offload old stuff on you for premium prices. 

Any general suggestions on Silver vs Copper, which cable placements will most likely make a difference as well as if I should replace the AC cables on any of the equipment (of course the Niagara  does not come with a power cable. Thats everything so far.  

My experience, many AQ models over many years:

• Silver is better - usually gives a good bit more detail without getting too bright. But the "bigger" silver models are usually better, as the entry level models can often be a little lean / lightweight and sterile by comparison. 
• Silver is worth it when you're searching for good deals on USED cables. However it's hard to justify their current "new" silver prices. In that case I'd say copper is more than good enough; use the saved money for other upgrades. 
• I found the best improvement from Hurricane PC's is on power amps. But I still really like the old NRG-1000 cords. I'm also quite happy with NRG-1000 type cords on all my source and preamp equipment.
• Speaker cables are #1 importance, then PC's on amps (and maybe Niagara) #2, then ICs and source PC's #3. 
• There are often great used deals on older AQ models but the lines are VERY confusing at first and you have to watch out for counterfeits - especially on certain models: Sky, K2, WEL Signature anything. And all the new stuff :( 

The Rocket 88 is a very good cable that represents a "sweet spot" of sorts for price-to-performance. Even on a modest system, I heard a big upgrade from 88 over Rocket 44 (both single biwire configuration, both modern versions, to be sure -- since Rocket production goes back many years). It's a good cable you can stick in any system in need of a good cable, and get good performance.

Above the 88 is where it gets tricky - system & preference matching becomes key. I've had my share or exotic older AQ silver cables (KE-4, Kilimanjaro x2, Everest x2, Wildwood x2, Thunderbird Zero). Sometimes, in some systems, the silver cables simply run away from 88's, revealing a large chasm of difference in detail and dynamics. Other times the 88's hold their own quite well; their natural warmth can actually be quite seductive. The Thunderbird Zero didn't do it for me -- I think, as they say, these really need to be the biwire version to show off. I wouldn't recommend just using the Zero as I did. AQ recommends William Tell bi-wire over Thunderbird Zero alone, and I believe them. 

“ …. Go buy some counterfeit cables. Hell they all are the same.…”

NOT SO …, Rather, counterfeit fake cables are usually crap builds,

Sadly I had my brain turned off, and inadvertently bought some counterfeit AQ King Cobra cables off ebay. They’re not super expensive cables, and I didn’t consider they might be counterfeits. I’m well familiar with higher end counterfeits on higher end AQ models, and have successfully avoided those to date.

Anyways, these counterfeit KC cables superficially look like the real thing (I own genuine pairs as well) - packaging, cables, connectors. However, the termination quality was truly awful. The metal XLR connectors fit together very poorly, and nothing was secured properly. Strain-relief nonexistent. No way I was putting that crap in any of my systems to test.

I can’t get on board with knowingly buying this Chinese knock-off garbage. They are NOT the same as genuine articles.