I Used the Castlerock with mine and loved them. I thought it made a big difference. They are internal bi wire type. I am thinking about moving up in the line though. I saw mike has the Aspen on his Quatro's and I like that idea but don't have any to audition. Once I figure that out, I'd be selling my Castlerocks (8') for nearly 50% off list probably.
Personally, I don't feel that any other brand of cable will make you as happy as what you have. The AQ cables are about as neutral as you get and they don't do anything wrong. When you start experimenting with some of the other cables, be it big name or boutique, you can run into problems I feel. I've had a ton of cable in and out just to hear. Every Nordost I've tried from Odin to Frey I think it was sounded way too bright. Kimber was the same for me. Cardas makes really good cable too, but to get the same performance as the AQ, you are in the same price range or more I feel.
Others may have better ideas, but you may want to find an equal run of 44's and do a double bi wire. Haven't heard that cable done that way, but the reason I may move up is because I'd also be getting a double run.